diff --git a/BGL/test/BGL/test_deprecated_io.cpp b/BGL/test/BGL/test_deprecated_io.cpp
index 0759dbc8f5b..65459a997fd 100644
--- a/BGL/test/BGL/test_deprecated_io.cpp
+++ b/BGL/test/BGL/test_deprecated_io.cpp
@@ -1,4 +1,5 @@
 #include <CGAL/Installation/internal/disable_deprecation_warnings_and_errors.h>
+
 #include <fstream>
 #include <iostream>
 #include <CGAL/Surface_mesh.h>
diff --git a/GraphicsView/include/CGAL/Buffer_for_vao.h b/GraphicsView/include/CGAL/Buffer_for_vao.h
index e0af44f8e89..e1093da21a7 100644
--- a/GraphicsView/include/CGAL/Buffer_for_vao.h
+++ b/GraphicsView/include/CGAL/Buffer_for_vao.h
@@ -15,7 +15,7 @@
 
 #include <CGAL/license/GraphicsView.h>
 
-#include <CGAL/Triangulation_2_projection_traits_3.h>
+#include <CGAL/Projection_traits_3.h>
 #include <CGAL/Triangulation_vertex_base_with_info_2.h>
 #include <CGAL/Triangulation_face_base_with_info_2.h>
 #include <CGAL/Constrained_Delaunay_triangulation_2.h>
@@ -887,7 +887,7 @@ protected:
     bool is_process;
   };
 
-  typedef CGAL::Triangulation_2_projection_traits_3<CGAL::Exact_predicates_inexact_constructions_kernel> P_traits;
+  typedef CGAL::Projection_traits_3<CGAL::Exact_predicates_inexact_constructions_kernel> P_traits;
   typedef CGAL::Triangulation_vertex_base_with_info_2<Vertex_info, P_traits> Vb;
   typedef CGAL::Triangulation_face_base_with_info_2<Face_info, P_traits>     Fb1;
   typedef CGAL::Constrained_triangulation_face_base_2<P_traits, Fb1>         Fb;
diff --git a/Installation/CHANGES.md b/Installation/CHANGES.md
index 77edf0ad8b7..8454502f810 100644
--- a/Installation/CHANGES.md
+++ b/Installation/CHANGES.md
@@ -39,6 +39,8 @@ Release date: December 2021
 -   Added `construct_centroid_2_object()` and `compute_determinant_2_object()` in `Projection_traits_xy_3`, `Projection_traits_xz_3`,
     and`Projection_traits_yz_3` classes.
 
+-   Added documentation for the class `Projection_traits_3`, which enables the use of 2D algorithms on the projections of 3D data onto an arbitrary plane.
+
 ### [Polygon Mesh Processing](https://doc.cgal.org/5.4/Manual/packages.html#PkgPolygonMeshProcessing)
 
 -   Added the function `CGAL::Polygon_mesh_processing::match_faces()`, which, given two polygon meshes,
diff --git a/Kernel_23/doc/Kernel_23/CGAL/Projection_traits_3.h b/Kernel_23/doc/Kernel_23/CGAL/Projection_traits_3.h
new file mode 100644
index 00000000000..36ee3865126
--- /dev/null
+++ b/Kernel_23/doc/Kernel_23/CGAL/Projection_traits_3.h
@@ -0,0 +1,51 @@
+namespace CGAL{
+
+/*!
+\ingroup kernel_classes
+
+The class `Projection_traits_3` works similarly to the `Projection_traits_xy_3`,
+`Projection_traits_xz_3`, and `Projection_traits_yz_3` traits classes, enabling
+the use of 2D algorithms on the projections of 3D data onto an arbitrary plane.
+
+\tparam K must be a model of `Kernel`
+
+\note Internal constructions (projections) are used in the predicate and
+construction functors of this class. If `K` is a model of `Kernel` providing exact
+constructions or if `K` is a `CGAL::Filtered_kernel` (such as for
+`CGAL::Exact_predicates_inexact_constructions_kernel`), this class automatically
+provides exact predicates.
+
+\cgalModels `TriangulationTraits_2`
+\cgalModels `DelaunayTriangulationTraits_2`
+\cgalModels `ConstrainedTriangulationTraits_2`
+\cgalModels `PolygonTraits_2`
+
+\sa `CGAL::Projection_traits_xy_3`
+\sa `CGAL::Projection_traits_xz_3`
+\sa `CGAL::Projection_traits_yz_3`
+*/
+template <class K>
+class Projection_traits_3
+{
+public:
+  /// \name Functors
+  /// The functors provided by this class are those listed in the
+  /// concepts. The functors operate on the 2D projections of their
+  /// arguments. They come with preconditions that projections of the
+  /// arguments are non-degenerate, e.g. a line segment does not project
+  /// on a single point, two points do not project onto the same point, etc.
+
+  /// \name Creation
+  ///@{
+
+  /*!
+   * \brief Constructor
+   *
+   * \param normal a vector orthogonal to the projection plane.
+   */
+  Projection_traits_3(const typename K::Vector_3& normal);
+
+  ///@}
+};
+
+} // end namespace CGAL
diff --git a/Kernel_23/doc/Kernel_23/CGAL/Projection_traits_xy_3.h b/Kernel_23/doc/Kernel_23/CGAL/Projection_traits_xy_3.h
index 67c3a96b0bd..bdda2985723 100644
--- a/Kernel_23/doc/Kernel_23/CGAL/Projection_traits_xy_3.h
+++ b/Kernel_23/doc/Kernel_23/CGAL/Projection_traits_xy_3.h
@@ -13,12 +13,13 @@ deal with projections on the
 `zx`- and the `zy`-plane,
 respectively.
 
-\cgalHeading{Parameters}
+\tparam K must be a model of `Kernel`.
 
-The template parameter `K` has to
-be instantiated by a model of the `Kernel` concept.
-`Projection_traits_xy_3` uses types
-and predicates defined in `K`.
+\note Internal constructions (projections) are used in the predicate and
+construction functors of this class. If `K` is a model of `Kernel` providing exact
+constructions or if `K` is a `CGAL::Filtered_kernel` (such as for
+`CGAL::Exact_predicates_inexact_constructions_kernel`), this class automatically
+provides exact predicates.
 
 \cgalModels The class is a model of several 2D triangulation traits class concepts,
   except that it does not provide the type and constructors
@@ -33,6 +34,7 @@ and predicates defined in `K`.
 \cgalModels `AnalyticWeightTraits_2`
 \cgalModels `BarycentricTraits_2`
 
+\sa `CGAL::Projection_traits_3`
 */
 template< typename K >
 class Projection_traits_xy_3 {
diff --git a/Kernel_23/doc/Kernel_23/Concepts/FunctionObjectConcepts.h b/Kernel_23/doc/Kernel_23/Concepts/FunctionObjectConcepts.h
index e9a5d9f3058..b83e4c7aa02 100644
--- a/Kernel_23/doc/Kernel_23/Concepts/FunctionObjectConcepts.h
+++ b/Kernel_23/doc/Kernel_23/Concepts/FunctionObjectConcepts.h
@@ -8898,7 +8898,7 @@ public:
 
   /*!
     returns true iff the \f$ x\f$-coordinate of `p` is smaller than the
-    \f$ x\f$-coordinate of `q` or if the are the same and
+    \f$ x\f$-coordinate of `q` or if they are the same and
     the \f$ y\f$-coordinate of `p` is smaller than the \f$ y\f$-coordinate of `q`, or,
     if both \f$ x\f$- and \f$ y\f$- coordinate are identical and
     the \f$ z\f$-coordinate of `p` is smaller than the \f$ z\f$-coordinate of `q`.
@@ -8928,7 +8928,7 @@ public:
 
   /*!
     returns true iff the \f$ x\f$-coordinate of `p` is smaller than the
-    \f$ x\f$-coordinate of `q` or if the are the same and
+    \f$ x\f$-coordinate of `q` or if they are the same and
     the \f$ y\f$-coordinate of `p` is smaller than the \f$ y\f$-coordinate of `q`.
   */
   bool operator()(const Kernel::Point_2&p,
@@ -8957,7 +8957,7 @@ public:
 
   /*!
     returns true iff the \f$ x\f$-coordinate of `p` is smaller than the
-    \f$ x\f$-coordinate of `q` or if the are the same and
+    \f$ x\f$-coordinate of `q` or if they are the same and
     the \f$ y\f$-coordinate of `p` is smaller than the \f$ y\f$-coordinate of `q`.
   */
   bool operator()(const Kernel::Point_3&p,
@@ -9040,7 +9040,7 @@ public:
 
   /*!
     returns true iff the \f$ y\f$-coordinate of `p` is smaller than the
-    \f$ y\f$-coordinate of `q` or if the are the same and
+    \f$ y\f$-coordinate of `q` or if they are the same and
     the \f$ x\f$-coordinate of `p` is smaller than the \f$ x\f$-coordinate of `q`.
   */
   bool operator()(const Kernel::Point_2&p,
diff --git a/Kernel_23/doc/Kernel_23/Doxyfile.in b/Kernel_23/doc/Kernel_23/Doxyfile.in
index 14a2e4d6328..b78b82fb7d0 100644
--- a/Kernel_23/doc/Kernel_23/Doxyfile.in
+++ b/Kernel_23/doc/Kernel_23/Doxyfile.in
@@ -2,3 +2,4 @@
 
 PROJECT_NAME = "CGAL ${CGAL_DOC_VERSION} - 2D and 3D Linear Geometry Kernel"
 EXAMPLE_PATH              +=  ${CGAL_Filtered_kernel_EXAMPLE_DIR}
+EXAMPLE_PATH              +=  ${CGAL_Triangulation_2_EXAMPLE_DIR}
diff --git a/Kernel_23/doc/Kernel_23/PackageDescription.txt b/Kernel_23/doc/Kernel_23/PackageDescription.txt
index 54fa6580087..873c5e089a1 100644
--- a/Kernel_23/doc/Kernel_23/PackageDescription.txt
+++ b/Kernel_23/doc/Kernel_23/PackageDescription.txt
@@ -71,6 +71,7 @@
 - `CGAL::Simple_cartesian<FieldNumberType>`
 - `CGAL::Simple_homogeneous<RingNumberType>`
 - `CGAL::Projection_traits_xy_3<K>`
+- `CGAL::Projection_traits_3<K>`
 
 \cgalCRPSection{Predefined Kernels}
 
diff --git a/Kernel_23/doc/Kernel_23/examples.txt b/Kernel_23/doc/Kernel_23/examples.txt
index 6b38afbd27a..7a089e79115 100644
--- a/Kernel_23/doc/Kernel_23/examples.txt
+++ b/Kernel_23/doc/Kernel_23/examples.txt
@@ -13,4 +13,5 @@
 \example Kernel_23/points_and_segment.cpp
 \example Kernel_23/surprising.cpp
 \example Kernel_23/exact.cpp
+\example Triangulation_2/triangulation_projection_traits.cpp
 */
diff --git a/Triangulation_2/include/CGAL/Triangulation_2/internal/Triangulation_2_filtered_projection_traits_3.h b/Kernel_23/include/CGAL/Kernel_23/internal/Filtered_projection_traits_3.h
similarity index 66%
rename from Triangulation_2/include/CGAL/Triangulation_2/internal/Triangulation_2_filtered_projection_traits_3.h
rename to Kernel_23/include/CGAL/Kernel_23/internal/Filtered_projection_traits_3.h
index 5bf5849d485..968caae994b 100644
--- a/Triangulation_2/include/CGAL/Triangulation_2/internal/Triangulation_2_filtered_projection_traits_3.h
+++ b/Kernel_23/include/CGAL/Kernel_23/internal/Filtered_projection_traits_3.h
@@ -5,30 +5,27 @@
 //
 // $URL$
 // $Id$
-// SPDX-License-Identifier: GPL-3.0-or-later OR LicenseRef-Commercial
+// SPDX-License-Identifier: LGPL-3.0-or-later OR LicenseRef-Commercial
 //
 //
 // Author(s)     : Laurent Rineau
 
 
-#ifndef CGAL_INTERNAL_TRIANGULATION_2_FILTERED_PROJECTION_TRAITS_3_H
-#define CGAL_INTERNAL_TRIANGULATION_2_FILTERED_PROJECTION_TRAITS_3_H
+#ifndef CGAL_INTERNAL_FILTERED_PROJECTION_TRAITS_3_H
+#define CGAL_INTERNAL_FILTERED_PROJECTION_TRAITS_3_H
 
-#include <CGAL/license/Triangulation_2.h>
-
-
-#include <CGAL/Triangulation_2/internal/Triangulation_2_projection_traits_base_3.h>
+#include <CGAL/Kernel_23/internal/Projection_traits_base_3.h>
 #include <CGAL/Filtered_predicate_with_state.h>
 
 namespace CGAL {
 
 template < class Filtered_kernel >
-class Triangulation_2_filtered_projection_traits_3
-  : public Triangulation_2_projection_traits_base_3<Filtered_kernel>
+class Filtered_projection_traits_3
+  : public Projection_traits_base_3<Filtered_kernel>
 {
   typedef Filtered_kernel K;
-  typedef Triangulation_2_filtered_projection_traits_3<K> Self;
-  typedef Triangulation_2_projection_traits_base_3<K> Base;
+  typedef Filtered_projection_traits_3<K> Self;
+  typedef Projection_traits_base_3<K> Base;
 
   typedef typename K::Exact_kernel Exact_kernel;
   typedef typename K::Approximate_kernel Approximate_kernel;
@@ -36,11 +33,11 @@ class Triangulation_2_filtered_projection_traits_3
   typedef typename K::C2F C2F;
 
 public:
-  typedef Triangulation_2_projection_traits_base_3<Exact_kernel> Exact_traits;
-  typedef Triangulation_2_projection_traits_base_3<Approximate_kernel> Filtering_traits;
+  typedef Projection_traits_base_3<Exact_kernel> Exact_traits;
+  typedef Projection_traits_base_3<Approximate_kernel> Filtering_traits;
 
 public:
-  explicit Triangulation_2_filtered_projection_traits_3(const typename K::Vector_3& n)
+  explicit Filtered_projection_traits_3(const typename K::Vector_3& n)
     : Base(n)
   {
   }
@@ -73,9 +70,9 @@ public:
   CGAL_TRIANGULATION_2_PROJ_TRAITS_FILTER_PRED(Compare_y_2,
                                                compare_y_2_object,
                                                base2)
-}; // end class Triangulation_2_projection_traits_base_3<Filtered_kernel>
+}; // end class Projection_traits_base_3<Filtered_kernel>
 
 } // end namespace CGAL
 
 
-#endif // CGAL_INTERNAL_TRIANGULATION_2_FILTERED_PROJECTION_TRAITS_3_H
+#endif // CGAL_INTERNAL_FILTERED_PROJECTION_TRAITS_3_H
diff --git a/Kernel_23/include/CGAL/Kernel_23/internal/Projection_traits_3.h b/Kernel_23/include/CGAL/Kernel_23/internal/Projection_traits_3.h
index 0cb5624bc74..d8c230c546c 100644
--- a/Kernel_23/include/CGAL/Kernel_23/internal/Projection_traits_3.h
+++ b/Kernel_23/include/CGAL/Kernel_23/internal/Projection_traits_3.h
@@ -833,6 +833,8 @@ public:
   }
 };
 
+// This is for projection traits along a specific canonical plane (xy, yz, xz)
+// The generic class for an arbitrary normal is CGAL::Projection_traits_3<K> (not in `internal`)
 template < class R, int dim >
 class Projection_traits_3 {
 public:
diff --git a/Triangulation_2/include/CGAL/Triangulation_2/internal/Triangulation_2_projection_traits_base_3.h b/Kernel_23/include/CGAL/Kernel_23/internal/Projection_traits_base_3.h
similarity index 96%
rename from Triangulation_2/include/CGAL/Triangulation_2/internal/Triangulation_2_projection_traits_base_3.h
rename to Kernel_23/include/CGAL/Kernel_23/internal/Projection_traits_base_3.h
index 5087c9516ae..6a59047bcec 100644
--- a/Triangulation_2/include/CGAL/Triangulation_2/internal/Triangulation_2_projection_traits_base_3.h
+++ b/Kernel_23/include/CGAL/Kernel_23/internal/Projection_traits_base_3.h
@@ -5,17 +5,14 @@
 //
 // $URL$
 // $Id$
-// SPDX-License-Identifier: GPL-3.0-or-later OR LicenseRef-Commercial
+// SPDX-License-Identifier: LGPL-3.0-or-later OR LicenseRef-Commercial
 //
 //
 // Author(s)     : Laurent Rineau
 
 
-#ifndef CGAL_INTERNAL_TRIANGULATION_2_PROJECTION_TRAITS_BASE_3_H
-#define CGAL_INTERNAL_TRIANGULATION_2_PROJECTION_TRAITS_BASE_3_H
-
-#include <CGAL/license/Triangulation_2.h>
-
+#ifndef CGAL_INTERNAL_PROJECTION_TRAITS_BASE_3_H
+#define CGAL_INTERNAL_PROJECTION_TRAITS_BASE_3_H
 
 #include <CGAL/Profile_timer.h>
 #include <CGAL/intersections.h>
@@ -379,9 +376,9 @@ public:
 
 
 template < class Kernel >
-class Triangulation_2_projection_traits_base_3
+class Projection_traits_base_3
 {
-  typedef Triangulation_2_projection_traits_base_3<Kernel> Self;
+  typedef Projection_traits_base_3<Kernel> Self;
 
   typename Kernel::Vector_3 n, b1, b2;
 
@@ -389,7 +386,7 @@ public:
   typedef typename Kernel::Vector_3 Vector_3;
 
 
-  explicit Triangulation_2_projection_traits_base_3(const Vector_3& n_)
+  explicit Projection_traits_base_3(const Vector_3& n_)
     : n(n_)
   {
     typedef typename Kernel::FT FT;
@@ -589,8 +586,8 @@ public:
     return Projection_to_plan(plane_point, *this);
   }
 
-}; // end class Triangulation_2_projection_traits_base_3<Kernel>
+}; // end class Projection_traits_base_3<Kernel>
 
 } // end namespace CGAL
 
-#endif // CGAL_INTERNAL_TRIANGULATION_2_PROJECTION_TRAITS_BASE_3_H
+#endif // CGAL_INTERNAL_PROJECTION_TRAITS_BASE_3_H
diff --git a/Kernel_23/include/CGAL/Projection_traits_3.h b/Kernel_23/include/CGAL/Projection_traits_3.h
new file mode 100644
index 00000000000..4deb40f0bce
--- /dev/null
+++ b/Kernel_23/include/CGAL/Projection_traits_3.h
@@ -0,0 +1,47 @@
+// Copyright (c) 2009  GeometryFactory (France)
+// All rights reserved.
+//
+// This file is part of CGAL (www.cgal.org).
+//
+// $URL$
+// $Id$
+// SPDX-License-Identifier: LGPL-3.0-or-later OR LicenseRef-Commercial
+//
+//
+// Author(s)     : Laurent Rineau
+
+
+#ifndef CGAL_PROJECTION_TRAITS_3_H
+#define CGAL_PROJECTION_TRAITS_3_H
+
+#include <CGAL/Kernel_23/internal/Filtered_projection_traits_3.h>
+
+namespace CGAL {
+
+// This declaration is needed to break the cyclic dependency.
+template < class Filtered_kernel >
+class Filtered_projection_traits_3;
+
+template <class Kernel, bool Has_filtered_predicates=Kernel::Has_filtered_predicates>
+class Projection_traits_3
+  : public Projection_traits_base_3<Kernel>
+{
+public:
+  explicit Projection_traits_3(const typename Kernel::Vector_3& n_)
+    : Projection_traits_base_3<Kernel>(n_)
+  {}
+};
+
+template <class Kernel>
+class Projection_traits_3<Kernel, true>
+  : public Filtered_projection_traits_3<Kernel>
+{
+public:
+  explicit Projection_traits_3(const typename Kernel::Vector_3& n_)
+    : Filtered_projection_traits_3<Kernel>(n_)
+  {}
+};
+
+} // namespace CGAL
+
+#endif // CGAL_PROJECTION_TRAITS_3_H
diff --git a/Linear_cell_complex/demo/Linear_cell_complex/typedefs.h b/Linear_cell_complex/demo/Linear_cell_complex/typedefs.h
index 459c745f1b9..d3d334865de 100644
--- a/Linear_cell_complex/demo/Linear_cell_complex/typedefs.h
+++ b/Linear_cell_complex/demo/Linear_cell_complex/typedefs.h
@@ -14,7 +14,7 @@
 
 #include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
 
-#include <CGAL/Triangulation_2_projection_traits_3.h>
+#include <CGAL/Projection_traits_3.h>
 #include <CGAL/Triangulation_vertex_base_with_info_2.h>
 #include <CGAL/Triangulation_face_base_with_info_2.h>
 #include <CGAL/Constrained_Delaunay_triangulation_2.h>
@@ -178,7 +178,7 @@ struct Face_info {
   bool is_process;
 };
 
-typedef CGAL::Triangulation_2_projection_traits_3<CGAL::Exact_predicates_inexact_constructions_kernel> P_traits;
+typedef CGAL::Projection_traits_3<CGAL::Exact_predicates_inexact_constructions_kernel> P_traits;
 typedef CGAL::Triangulation_vertex_base_with_info_2<Vertex_info, P_traits> Vb;
 
 typedef CGAL::Triangulation_face_base_with_info_2<Face_info,P_traits> Fb1;
diff --git a/Linear_cell_complex/examples/Linear_cell_complex/basic_viewer.h b/Linear_cell_complex/examples/Linear_cell_complex/basic_viewer.h
index cbc75458f95..9725e3d5960 100644
--- a/Linear_cell_complex/examples/Linear_cell_complex/basic_viewer.h
+++ b/Linear_cell_complex/examples/Linear_cell_complex/basic_viewer.h
@@ -22,7 +22,7 @@
 #include <QGLBuffer>
 #include <QOpenGLShaderProgram>
 
-#include <CGAL/Triangulation_2_projection_traits_3.h>
+#include <CGAL/Projection_traits_3.h>
 #include <CGAL/Triangulation_vertex_base_with_info_2.h>
 #include <CGAL/Triangulation_face_base_with_info_2.h>
 #include <CGAL/Constrained_Delaunay_triangulation_2.h>
@@ -211,7 +211,7 @@ class Basic_viewer : public CGAL::QGLViewer, public QOpenGLFunctions
     bool is_process;
   };
 
-  typedef CGAL::Triangulation_2_projection_traits_3<CGAL::Exact_predicates_inexact_constructions_kernel> P_traits;
+  typedef CGAL::Projection_traits_3<CGAL::Exact_predicates_inexact_constructions_kernel> P_traits;
   typedef CGAL::Triangulation_vertex_base_with_info_2<Vertex_info, P_traits> Vb;
 
   typedef CGAL::Triangulation_face_base_with_info_2<Face_info, P_traits> Fb1;
diff --git a/Mesh_2/test/Mesh_2/test_mesh_projection_traits.cpp b/Mesh_2/test/Mesh_2/test_mesh_projection_traits.cpp
index 030471c0295..63ed376d7af 100644
--- a/Mesh_2/test/Mesh_2/test_mesh_projection_traits.cpp
+++ b/Mesh_2/test/Mesh_2/test_mesh_projection_traits.cpp
@@ -3,12 +3,12 @@
 #include <CGAL/Delaunay_mesher_2.h>
 #include <CGAL/Delaunay_mesh_face_base_2.h>
 #include <CGAL/Delaunay_mesh_size_criteria_2.h>
-#include <CGAL/Triangulation_2_projection_traits_3.h>
+#include <CGAL/Projection_traits_3.h>
 
 #include <iostream>
 
 typedef CGAL::Exact_predicates_inexact_constructions_kernel K1;
-typedef CGAL::Triangulation_2_projection_traits_3<K1> K;
+typedef CGAL::Projection_traits_3<K1> K;
 typedef CGAL::Triangulation_vertex_base_2<K> Vb;
 typedef CGAL::Delaunay_mesh_face_base_2<K> Fb;
 typedef CGAL::Triangulation_data_structure_2<Vb, Fb> Tds;
diff --git a/Nef_3/include/CGAL/boost/graph/convert_nef_polyhedron_to_polygon_mesh.h b/Nef_3/include/CGAL/boost/graph/convert_nef_polyhedron_to_polygon_mesh.h
index 5f651edb1ab..dd289b6d3f3 100644
--- a/Nef_3/include/CGAL/boost/graph/convert_nef_polyhedron_to_polygon_mesh.h
+++ b/Nef_3/include/CGAL/boost/graph/convert_nef_polyhedron_to_polygon_mesh.h
@@ -22,7 +22,7 @@
 #include <CGAL/Cartesian_converter.h>
 #include <boost/unordered_map.hpp>
 #include <CGAL/Constrained_Delaunay_triangulation_2.h>
-#include <CGAL/Triangulation_2_projection_traits_3.h>
+#include <CGAL/Projection_traits_3.h>
 #include <CGAL/Triangulation_vertex_base_with_info_2.h>
 #include <CGAL/Triangulation_face_base_with_info_2.h>
 #include <CGAL/Kernel/global_functions_3.h>
@@ -210,8 +210,8 @@ struct Shell_polygons_visitor
     }
 
     // cases where a cdt is needed
-    typedef typename Nef_polyhedron::Kernel Kernel;
-    typedef Triangulation_2_projection_traits_3<Kernel>            P_traits;
+    typedef typename Nef_polyhedron::Kernel                              Kernel;
+    typedef Projection_traits_3<Kernel>                                  P_traits;
     typedef Triangulation_vertex_base_with_info_2<std::size_t, P_traits> Vb;
     typedef Triangulation_face_base_with_info_2<FaceInfo2,P_traits>     Fbb;
     typedef Constrained_triangulation_face_base_2<P_traits,Fbb>          Fb;
diff --git a/Polygon_mesh_processing/include/CGAL/Polygon_mesh_processing/internal/Corefinement/Visitor.h b/Polygon_mesh_processing/include/CGAL/Polygon_mesh_processing/internal/Corefinement/Visitor.h
index 77b5404b298..7e7bfd600a1 100644
--- a/Polygon_mesh_processing/include/CGAL/Polygon_mesh_processing/internal/Corefinement/Visitor.h
+++ b/Polygon_mesh_processing/include/CGAL/Polygon_mesh_processing/internal/Corefinement/Visitor.h
@@ -23,7 +23,7 @@
 #include <CGAL/Default.h>
 #include <CGAL/boost/graph/Euler_operations.h>
 #include <CGAL/Constrained_Delaunay_triangulation_2.h>
-#include <CGAL/Triangulation_2_projection_traits_3.h>
+#include <CGAL/Projection_traits_3.h>
 #include <CGAL/Triangulation_vertex_base_with_info_2.h>
 
 #include <boost/container/flat_map.hpp>
@@ -387,9 +387,9 @@ private:
    typedef Non_manifold_feature_map<TriangleMesh>               NM_features_map;
 // typedef for the CDT
    typedef Intersection_nodes<TriangleMesh, VertexPointMap1, VertexPointMap2,
-            Predicates_on_constructions_needed>                          INodes;
+            Predicates_on_constructions_needed>                              INodes;
    typedef typename INodes::Exact_kernel                                     EK;
-    typedef Triangulation_2_projection_traits_3<EK>                  CDT_traits;
+    typedef Projection_traits_3<EK>                                          CDT_traits;
     typedef Triangulation_vertex_base_with_info_2<Node_id,CDT_traits>        Vb;
     typedef Constrained_triangulation_face_base_2<CDT_traits>                Fb;
     typedef Triangulation_data_structure_2<Vb,Fb>                         TDS_2;
diff --git a/Polygon_mesh_processing/include/CGAL/Polygon_mesh_processing/internal/Hole_filling/Triangulate_hole_polyline.h b/Polygon_mesh_processing/include/CGAL/Polygon_mesh_processing/internal/Hole_filling/Triangulate_hole_polyline.h
index 4f1e2b7fac8..a28b3e2c826 100644
--- a/Polygon_mesh_processing/include/CGAL/Polygon_mesh_processing/internal/Hole_filling/Triangulate_hole_polyline.h
+++ b/Polygon_mesh_processing/include/CGAL/Polygon_mesh_processing/internal/Hole_filling/Triangulate_hole_polyline.h
@@ -28,7 +28,7 @@
 #include <CGAL/Triangulation_vertex_base_with_info_2.h>
 #include <CGAL/Triangulation_face_base_with_info_2.h>
 #include <CGAL/Constrained_Delaunay_triangulation_2.h>
-#include <CGAL/Triangulation_2_projection_traits_3.h>
+#include <CGAL/Projection_traits_3.h>
 #include <queue>
 #endif
 
@@ -1374,7 +1374,7 @@ triangulate_hole_polyline_with_cdt(const PointRange& points,
   }
 
   // Checking the hole simplicity.
-  typedef Triangulation_2_projection_traits_3<Traits> P_traits;
+  typedef CGAL::Projection_traits_3<Traits> P_traits;
   const P_traits p_traits(avg_normal);
   if (!is_simple_2(P.begin(), P.end() - 1, p_traits)) {
     // std::cerr << "WARNING: simplicity, cdt 2 falls back to the original solution!" << std::endl;
diff --git a/Polygon_mesh_processing/include/CGAL/Polygon_mesh_processing/triangulate_faces.h b/Polygon_mesh_processing/include/CGAL/Polygon_mesh_processing/triangulate_faces.h
index a4c38c7b040..a2cc56ae520 100644
--- a/Polygon_mesh_processing/include/CGAL/Polygon_mesh_processing/triangulate_faces.h
+++ b/Polygon_mesh_processing/include/CGAL/Polygon_mesh_processing/triangulate_faces.h
@@ -24,7 +24,7 @@
 #include <CGAL/Triangulation_vertex_base_with_info_2.h>
 #include <CGAL/Triangulation_face_base_with_info_2.h>
 #include <CGAL/Constrained_Delaunay_triangulation_2.h>
-#include <CGAL/Triangulation_2_projection_traits_3.h>
+#include <CGAL/Projection_traits_3.h>
 #else
 #include <CGAL/use.h>
 #endif
@@ -152,7 +152,7 @@ public:
 #ifndef CGAL_TRIANGULATE_FACES_DO_NOT_USE_CDT2
       if (use_cdt)
       {
-        typedef CGAL::Triangulation_2_projection_traits_3<Traits>   P_traits;
+        typedef CGAL::Projection_traits_3<Traits>   P_traits;
         typedef CGAL::Triangulation_vertex_base_with_info_2<halfedge_descriptor,
                                                             P_traits>        Vb;
         typedef CGAL::Triangulation_face_base_with_info_2<Face_info,
diff --git a/Polyhedron/demo/Polyhedron/Scene_lcc_item.cpp b/Polyhedron/demo/Polyhedron/Scene_lcc_item.cpp
index 7f23074391d..ae1e69a55a7 100644
--- a/Polyhedron/demo/Polyhedron/Scene_lcc_item.cpp
+++ b/Polyhedron/demo/Polyhedron/Scene_lcc_item.cpp
@@ -154,7 +154,7 @@ struct lcc_priv{
         bool is_process;
       };
 
-      typedef CGAL::Triangulation_2_projection_traits_3<CGAL::Exact_predicates_inexact_constructions_kernel> P_traits;
+      typedef CGAL::Projection_traits_3<CGAL::Exact_predicates_inexact_constructions_kernel> P_traits;
       typedef CGAL::Triangulation_vertex_base_with_info_2<Vertex_info, P_traits> Vb;
       typedef CGAL::Triangulation_face_base_with_info_2<Face_info, P_traits>     Fb1;
       typedef CGAL::Constrained_triangulation_face_base_2<P_traits, Fb1>         Fb;
diff --git a/Polyhedron/demo/Polyhedron/Scene_nef_polyhedron_item.cpp b/Polyhedron/demo/Polyhedron/Scene_nef_polyhedron_item.cpp
index 0595dc7956b..27ec846f35c 100644
--- a/Polyhedron/demo/Polyhedron/Scene_nef_polyhedron_item.cpp
+++ b/Polyhedron/demo/Polyhedron/Scene_nef_polyhedron_item.cpp
@@ -18,7 +18,7 @@
 #include <CGAL/minkowski_sum_3.h>
 #include <CGAL/convex_decomposition_3.h>
 
-#include <CGAL/Triangulation_2_projection_traits_3.h>
+#include <CGAL/Projection_traits_3.h>
 #include <CGAL/Triangulation_vertex_base_with_info_2.h>
 #include <CGAL/Triangulation_face_base_with_info_2.h>
 #include <CGAL/boost/graph/convert_nef_polyhedron_to_polygon_mesh.h>
@@ -33,7 +33,7 @@ typedef Point_container Pc;
 
 typedef Nef_polyhedron::Traits Traits;
 typedef Nef_polyhedron::Halffacet Facet;
-typedef CGAL::Triangulation_2_projection_traits_3<Traits>   P_traits;
+typedef CGAL::Projection_traits_3<Traits>   P_traits;
 typedef Nef_polyhedron::Halfedge_const_handle Halfedge_handle;
 struct Face_info {
     Nef_polyhedron::Halfedge_const_handle e[3];
diff --git a/Polyhedron/demo/Polyhedron/triangulate_primitive.h b/Polyhedron/demo/Polyhedron/triangulate_primitive.h
index 417fcd94899..c80ceb08aca 100644
--- a/Polyhedron/demo/Polyhedron/triangulate_primitive.h
+++ b/Polyhedron/demo/Polyhedron/triangulate_primitive.h
@@ -3,7 +3,7 @@
 #include <CGAL/Triangulation_vertex_base_with_info_2.h>
 #include <CGAL/Triangulation_face_base_with_info_2.h>
 #include <CGAL/Constrained_Delaunay_triangulation_2.h>
-#include <CGAL/Triangulation_2_projection_traits_3.h>
+#include <CGAL/Projection_traits_3.h>
 #include <CGAL/Three/Scene_item.h>
 #include <queue>
 
@@ -20,7 +20,7 @@ class FacetTriangulator
  typedef typename Kernel::Vector_3 Vector;
 
 
- typedef CGAL::Triangulation_2_projection_traits_3<Traits>   P_traits;
+ typedef CGAL::Projection_traits_3<Traits>   P_traits;
 
  typedef CGAL::Triangulation_vertex_base_with_info_2<halfedge_descriptor,
                                                      P_traits>        Vb;
diff --git a/Triangulation_2/doc/Triangulation_2/Triangulation_2.txt b/Triangulation_2/doc/Triangulation_2/Triangulation_2.txt
index a1c278c5a0b..6ad2276174e 100644
--- a/Triangulation_2/doc/Triangulation_2/Triangulation_2.txt
+++ b/Triangulation_2/doc/Triangulation_2/Triangulation_2.txt
@@ -487,7 +487,9 @@ See Section \ref Section_2D_Triangulations_Delaunay for an example.
 `Projection_traits_xz_3<R>` to
 deal with projections on the
 `yz` plane and `xz`-plane,
-respectively.
+respectively, as well as the geometric traits class
+`Projection_traits_3<R>` that deals with projections onto an
+arbitrary plane defined by its orthogonal vector.
 
 \subsection Subsection_2D_Triangulations_Basic_Example Example of a Basic Triangulation
 
diff --git a/Triangulation_2/examples/Triangulation_2/triangulation_projection_traits.cpp b/Triangulation_2/examples/Triangulation_2/triangulation_projection_traits.cpp
new file mode 100644
index 00000000000..73662c0eba7
--- /dev/null
+++ b/Triangulation_2/examples/Triangulation_2/triangulation_projection_traits.cpp
@@ -0,0 +1,39 @@
+#include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
+#include <CGAL/Constrained_Delaunay_triangulation_2.h>
+#include <CGAL/Projection_traits_3.h>
+
+#include <iostream>
+#include <vector>
+
+typedef CGAL::Exact_predicates_inexact_constructions_kernel                K;
+typedef CGAL::Projection_traits_3<K>                                       GT;
+
+typedef CGAL::Exact_predicates_tag                                         Itag;
+typedef CGAL::Constrained_Delaunay_triangulation_2<GT, CGAL::Default, Itag> CDT;
+typedef CDT::Point                                                         Point;
+typedef CDT::Edge                                                          Edge;
+
+int main()
+{
+  //4 points on the diagonal plane of a cube
+  std::vector<Point> ps(4);
+  ps[0] = Point(0,0,0);
+  ps[1] = Point(3,1,-1);
+  ps[2] = Point(-1, 3, -3);
+  ps[3] = Point(1,0.5,-0.5);
+
+  GT gt{ { 0, 1, 1} };
+  CDT cdt(gt);
+  for(int i = 0; i< 4; ++i)
+    cdt.insert(ps[i]);
+
+  for(int i = 1; i < 3; ++i)
+    cdt.insert_constraint(ps[i], ps[i+1]);
+
+  for(CDT::Face_handle f : cdt.all_face_handles())
+  {
+   for(int i=0; i<3; ++i)
+     std::cout << f->vertex(i)->point() << " ";
+   std::cout << std::endl;
+  }
+}
diff --git a/Triangulation_2/include/CGAL/Triangulation_2_projection_traits_3.h b/Triangulation_2/include/CGAL/Triangulation_2_projection_traits_3.h
index de475d6f44c..683c6d42153 100644
--- a/Triangulation_2/include/CGAL/Triangulation_2_projection_traits_3.h
+++ b/Triangulation_2/include/CGAL/Triangulation_2_projection_traits_3.h
@@ -10,43 +10,46 @@
 //
 // Author(s)     : Laurent Rineau
 
-
 #ifndef CGAL_TRIANGULATION_2_PROJECTION_TRAITS_3_H
 #define CGAL_TRIANGULATION_2_PROJECTION_TRAITS_3_H
 
 #include <CGAL/license/Triangulation_2.h>
 
+#define CGAL_DEPRECATED_HEADER "<CGAL/Triangulation_2_projection_traits_3.h>"
+#define CGAL_REPLACEMENT_HEADER "<CGAL/Projection_traits_3.h>"
+#include <CGAL/Installation/internal/deprecation_warning.h>
 
-#include <CGAL/Triangulation_2/internal/Triangulation_2_filtered_projection_traits_3.h>
+#ifndef CGAL_NO_DEPRECATED_CODE
 
-namespace CGAL{
+#include <CGAL/Kernel_23/internal/Filtered_projection_traits_3.h>
+
+namespace CGAL {
 
-// This declaration is needed to break the cyclic dependency.
 template < class Filtered_kernel >
-class Triangulation_2_filtered_projection_traits_3;
+class Filtered_projection_traits_3;
 
-template <class Kernel, bool Has_filtered_predicates=Kernel::Has_filtered_predicates>
+template <class Kernel, bool Has_filtered_predicates = Kernel::Has_filtered_predicates>
 class Triangulation_2_projection_traits_3
-  : public Triangulation_2_projection_traits_base_3<Kernel>
+  : public Projection_traits_base_3<Kernel>
 {
 public:
-  explicit
-  Triangulation_2_projection_traits_3(const typename Kernel::Vector_3& n_)
-    : Triangulation_2_projection_traits_base_3<Kernel>(n_)
+  explicit Triangulation_2_projection_traits_3(const typename Kernel::Vector_3& n_)
+    : Projection_traits_base_3<Kernel>(n_)
   {}
 };
 
 template <class Kernel>
 class Triangulation_2_projection_traits_3<Kernel, true>
-  : public Triangulation_2_filtered_projection_traits_3<Kernel>
+  : public Filtered_projection_traits_3<Kernel>
 {
 public:
-  explicit
-  Triangulation_2_projection_traits_3(const typename Kernel::Vector_3& n_)
-    : Triangulation_2_filtered_projection_traits_3<Kernel>(n_)
+  explicit Triangulation_2_projection_traits_3(const typename Kernel::Vector_3& n_)
+    : Filtered_projection_traits_3<Kernel>(n_)
   {}
 };
 
 } // end namespace CGAL
 
+#endif //CGAL_NO_DEPRECATED_CODE
+
 #endif // CGAL_TRIANGULATION_2_PROJECTION_TRAITS_3_H
diff --git a/Triangulation_2/test/Triangulation_2/CMakeLists.txt b/Triangulation_2/test/Triangulation_2/CMakeLists.txt
index 392f79e71b6..54c09717f8f 100644
--- a/Triangulation_2/test/Triangulation_2/CMakeLists.txt
+++ b/Triangulation_2/test/Triangulation_2/CMakeLists.txt
@@ -29,5 +29,6 @@ if(BUILD_TESTING)
     execution___of__test_regular_triangulation_2
     execution___of__test_const_del_triangulation_2
     execution___of__test_regular_hierarchy_2
+    execution___of__test_deprecated_projection_traits
     PROPERTIES RESOURCE_LOCK Triangulation_2_Tests_IO)
 endif()
diff --git a/Triangulation_2/test/Triangulation_2/test_cdt_2_projection_traits_special_case.cpp b/Triangulation_2/test/Triangulation_2/test_cdt_2_projection_traits_special_case.cpp
index bf163771380..1f6638de00e 100644
--- a/Triangulation_2/test/Triangulation_2/test_cdt_2_projection_traits_special_case.cpp
+++ b/Triangulation_2/test/Triangulation_2/test_cdt_2_projection_traits_special_case.cpp
@@ -1,13 +1,15 @@
 #include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
 #include <CGAL/Exact_predicates_exact_constructions_kernel.h>
+
 #include <CGAL/Constrained_Delaunay_triangulation_2.h>
-#include <CGAL/Triangulation_2_projection_traits_3.h>
+#include <CGAL/Projection_traits_3.h>
+
+#include <CGAL/Installation/internal/disable_deprecation_warnings_and_errors.h>
 #include <CGAL/Triangulation_2_projection_traits_3.h>
 
 #include <string>
 #include <fstream>
 
-
 typedef const double vec[3];
 const vec input[10] =
 { { -0.37503900000000001, 0.5, 0.47710999999999998                     },
@@ -128,20 +130,10 @@ int main()
   typedef CGAL::Exact_predicates_inexact_constructions_kernel Epick;
 
   bool ok = true;
-  ok = ok &&
-      test<CGAL::Epick,
-           CGAL::Triangulation_2_projection_traits_3<Epick> >
-      ("CDT_2 in a 3D plane, with Epick");
-  ok = ok &&
-      test<CGAL::Epeck,
-           CGAL::Triangulation_2_projection_traits_3<Epeck> >
-      ("CDT_2 in a 3D plane, with Epeck");
-  ok = ok && test_segment_intersections<CGAL::Epick,
-           CGAL::Triangulation_2_projection_traits_3<Epick> >
-      ("CDT_2 traits intersection with Epick");
-  ok = ok && test_segment_intersections<CGAL::Epeck,
-           CGAL::Triangulation_2_projection_traits_3<Epeck> >
-      ("CDT_2 traits intersection with Epeck");
+  ok = ok && test<CGAL::Epick, CGAL::Projection_traits_3<Epick> >("CDT_2 in a 3D plane, with Epick");
+  ok = ok && test<CGAL::Epeck, CGAL::Projection_traits_3<Epeck> >("CDT_2 in a 3D plane, with Epeck");
+  ok = ok && test_segment_intersections<CGAL::Epick, CGAL::Triangulation_2_projection_traits_3<Epick> >("CDT_2 traits intersection with Epick");
+  ok = ok && test_segment_intersections<CGAL::Epeck, CGAL::Triangulation_2_projection_traits_3<Epeck> >("CDT_2 traits intersection with Epeck");
 
   return ok ? 0 : 1;
 }
diff --git a/Triangulation_2/test/Triangulation_2/test_deprecated_projection_traits.cpp b/Triangulation_2/test/Triangulation_2/test_deprecated_projection_traits.cpp
new file mode 100644
index 00000000000..84a8465162d
--- /dev/null
+++ b/Triangulation_2/test/Triangulation_2/test_deprecated_projection_traits.cpp
@@ -0,0 +1,34 @@
+#include <CGAL/Installation/internal/disable_deprecation_warnings_and_errors.h>
+
+#include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
+#include <CGAL/Constrained_Delaunay_triangulation_2.h>
+#include <CGAL/Triangulation_2_projection_traits_3.h>
+
+#include <iostream>
+#include <vector>
+
+typedef CGAL::Exact_predicates_inexact_constructions_kernel                K;
+typedef CGAL::Triangulation_2_projection_traits_3<K>                       GT;
+
+typedef CGAL::Exact_predicates_tag                                         Itag;
+typedef CGAL::Constrained_Delaunay_triangulation_2<GT, CGAL::Default, Itag> CDT;
+typedef CDT::Point                                                         Point;
+typedef CDT::Edge                                                          Edge;
+
+int main()
+{
+  //4 points on the diagonal plane of a cube
+  std::vector<Point> ps(4);
+  ps[0] = Point(0,0,0);
+  ps[1] = Point(3,1,-1);
+  ps[2] = Point(-1, 3, -3);
+  ps[3] = Point(1,0.5,-0.5);
+
+  GT gt{ { 0, 1, 1} };
+  CDT cdt(gt);
+  for(int i = 0; i< 4; ++i)
+    cdt.insert(ps[i]);
+
+  for(int i = 1; i < 3; ++i)
+    cdt.insert_constraint(ps[i], ps[i+1]);
+}