diff --git a/Arrangement_on_surface_2/include/CGAL/Arr_tags.h b/Arrangement_on_surface_2/include/CGAL/Arr_tags.h
index 1aac0615585..8ba336b1e19 100644
--- a/Arrangement_on_surface_2/include/CGAL/Arr_tags.h
+++ b/Arrangement_on_surface_2/include/CGAL/Arr_tags.h
@@ -252,7 +252,7 @@ template <typename ArrSideCategory>
 struct Arr_is_side_oblivious {
   typedef ArrSideCategory                                       Side_cat;
   typedef std::is_same<Side_cat, Arr_oblivious_side_tag>        Is_same;
-  typedef std::conditional<Is_same::value, Arr_true, Arr_false> result;
+  typedef std::bool_constant<Is_same::value>                    result;
   typedef typename result::type                                 type;
 };
 
@@ -260,7 +260,7 @@ template <typename ArrSideCategory>
 struct Arr_is_side_open {
   typedef ArrSideCategory                                       Side_cat;
   typedef std::is_same<Side_cat, Arr_open_side_tag>             Is_same;
-  typedef std::conditional<Is_same,::value Arr_true, Arr_false> result;
+  typedef std::bool_constant<Is_same::value>                    result;
   typedef typename result::type                                 type;
 };
 
@@ -268,7 +268,7 @@ template <typename ArrSideCategory>
 struct Arr_is_side_identified {
   typedef ArrSideCategory                                       Side_cat;
   typedef std::is_same<Side_cat, Arr_identified_side_tag>       Is_same;
-  typedef std::conditional<Is_same::value, Arr_true, Arr_false> result;
+  typedef std::bool_constant<Is_same::value>                    result;
   typedef typename result::type                                 type;
 };
 
@@ -276,7 +276,7 @@ template <typename ArrSideCategory>
 struct Arr_is_side_contracted {
   typedef ArrSideCategory                                       Side_cat;
   typedef std::is_same<Side_cat, Arr_contracted_side_tag>       Is_same;
-  typedef std::conditional<Is_same::value, Arr_true, Arr_false> result;
+  typedef std::bool_constant<Is_same::value>                    result;
   typedef typename result::type                                 type;
 };
 
@@ -284,7 +284,7 @@ template <typename ArrSideCategory>
 struct Arr_is_side_closed {
   typedef ArrSideCategory                                       Side_cat;
   typedef std::is_same<Side_cat, Arr_closed_side_tag>           Is_same;
-  typedef std::conditional<Is_same::value, Arr_true, Arr_false> result;
+  typedef std::bool_constant<Is_same::value>                    result;
   typedef typename result::type                                 type;
 };
 
@@ -423,11 +423,12 @@ struct Arr_sane_identified_tagging {
   typedef boost::mpl::or_<LR_ide, LR_not_ide>           LR_ok;
   typedef boost::mpl::or_<BT_ide, BT_not_ide>           BT_ok;
 
-  /*! Boolean tag that is bool_<true> if opposite sides are either
+  /*! Boolean tag that is bool_constant<true> if opposite sides are either
    * both identified or both not-identified,
-   * otherwise bool_<false>
+   * otherwise bool_constant<false>
    */
-  typedef boost::mpl::and_<LR_ok, BT_ok>                result;
+  typedef std::bool_constant<LR_ok::value &&
+                             BT_ok::value>              result;
   static constexpr bool value = result::value;
 };
 
@@ -447,10 +448,10 @@ struct Arr_has_identified_sides {
   typedef typename Arr_is_side_identified<Side_one_cat>::result Side_one_ide;
   typedef typename Arr_is_side_identified<Side_two_cat>::result Side_two_ide;
 
-  /*! Boolean tag that is bool_<true> if one side is identified,
-   * otherwise bool_<false>
+  /*! Boolean tag that is bool_constant<true> if one side is identified,
+   * otherwise bool_constant<false>
    */
-  typedef boost::mpl::or_<Side_one_ide, Side_two_ide>   result;
+  typedef std::bool_constant<Side_one_ide::value || Side_two_ide::value> result;
 };
 
 /*! Checks whether one of two boundary sides are contracted
@@ -463,10 +464,11 @@ struct Arr_has_contracted_sides_two {
   typedef typename Arr_is_side_contracted<Side_one_cat>::result Side_one_con;
   typedef typename Arr_is_side_contracted<Side_two_cat>::result Side_two_con;
 
-  /*!\ Boolean tag that is bool_<true> if one side is identified,
-   * otherwise bool_<false>
+  /*!\ Boolean tag that is bool_constant<true> if one side is identified,
+   * otherwise bool_constant<false>
    */
-  typedef boost::mpl::or_<Side_one_con, Side_two_con>           result;
+  typedef std::bool_constant<Side_one_con::value ||
+                             Side_two_con::value>               result;
 };
 
 /*! Checks whether one of two boundary sides are closed
@@ -479,10 +481,11 @@ struct Arr_has_closed_sides_two {
   typedef typename Arr_is_side_closed<Side_one_cat>::result     Side_one_clo;
   typedef typename Arr_is_side_closed<Side_two_cat>::result     Side_two_clo;
 
-  /*! Boolean tag that is bool_<true> if one side is identified,
-   * otherwise bool_<false>
+  /*! Boolean tag that is bool_constant<true> if one side is identified,
+   * otherwise bool_constant<false>
    */
-  typedef boost::mpl::or_<Side_one_clo, Side_two_clo>           result;
+  typedef std::bool_constant<Side_one_clo::value ||
+                             Side_two_clo::value>               result;
 };
 
 /*! Checks whether one of two boundary sides are open
@@ -495,10 +498,11 @@ struct Arr_has_open_sides_two {
   typedef typename Arr_is_side_open<Side_one_cat>::result       Side_one_ope;
   typedef typename Arr_is_side_open<Side_two_cat>::result       Side_two_ope;
 
-  /*! Boolean tag that is bool_<true> if one side is identified,
-   * otherwise bool_<false>
+  /*! Boolean tag that is bool_constant<true> if one side is identified,
+   * otherwise bool_constant<false>
    */
-  typedef boost::mpl::or_<Side_one_ope, Side_two_ope>           result;
+  typedef std::bool_constant<Side_one_ope::value ||
+                             Side_two_ope::value>               result;
 };
 
 /*! Categorizes two boundary sides:
diff --git a/Arrangement_on_surface_2/include/CGAL/Arrangement_2/Arr_traits_adaptor_2_dispatching.h b/Arrangement_on_surface_2/include/CGAL/Arrangement_2/Arr_traits_adaptor_2_dispatching.h
index 283b2dc66b5..9bcabf985d6 100644
--- a/Arrangement_on_surface_2/include/CGAL/Arrangement_2/Arr_traits_adaptor_2_dispatching.h
+++ b/Arrangement_on_surface_2/include/CGAL/Arrangement_2/Arr_traits_adaptor_2_dispatching.h
@@ -58,11 +58,11 @@ public:
 
 private:
 
-  typedef std::conditional<
+  typedef std::conditional_t<
        std::is_same_v< Arr_smaller_implementation_tag, Arr_use_traits_tag >,
        std::true_type, std::false_type > Smaller_traits;
 
-  typedef std::conditional_t_<
+  typedef std::conditional_t<
        std::is_same_v< Arr_larger_implementation_tag, Arr_use_traits_tag >,
        std::true_type, std::false_type > Larger_traits;
 
@@ -71,7 +71,8 @@ public:
   //! the result type (if one side asks for traits, then ask traits!
   //! Or vice versa: If both ask for dummy, then dummy!)
   typedef std::conditional_t<
-              Smaller_traits, Larger_traits >::value || Arr_use_traits_tag::value,
+              Smaller_traits::value || Larger_traits::value,
+              Arr_use_traits_tag,
               Arr_use_dummy_tag > type;
 
 };
diff --git a/Arrangement_on_surface_2/include/CGAL/Arrangement_2/Arrangement_on_surface_2_global.h b/Arrangement_on_surface_2/include/CGAL/Arrangement_2/Arrangement_on_surface_2_global.h
index ee072c95778..5bc8054c525 100644
--- a/Arrangement_on_surface_2/include/CGAL/Arrangement_2/Arrangement_on_surface_2_global.h
+++ b/Arrangement_on_surface_2/include/CGAL/Arrangement_2/Arrangement_on_surface_2_global.h
@@ -64,7 +64,7 @@ namespace Ss2 = Surface_sweep_2;
 //
 // error: no matching function for call to `do_intersect(Arrangement_2<>&,
 // const Arr_segment_2&, const Arr_walk_along_line_point_location<>&,
-// mpl_::bool_< true>)'
+// std::bool_constant< true>)'
 //
 template <typename GeometryTraits_2, typename TopologyTraits,
           typename PointLocation, typename ZoneVisitor>
@@ -135,7 +135,7 @@ void insert(Arrangement_on_surface_2<GeometryTraits_2, TopologyTraits>& arr,
 //
 // error: no matching function for call to `do_intersect(Arrangement_2<>&,
 // const Arr_segment_2&, const Arr_walk_along_line_point_location<>&,
-// mpl_::bool_< true>)'
+// std::bool_constant< true>)'
 //
 //
 template <typename GeometryTraits_2, typename TopologyTraits,
@@ -409,7 +409,7 @@ void insert_non_empty(Arrangement_on_surface_2<GeometryTraits_2,
 //
 // error: no matching function for call to `do_intersect(Arrangement_2<>&,
 // const Arr_segment_2&, const Arr_walk_along_line_point_location<>&,
-// mpl_::bool_< true>)'
+// std::bool_constant< true>)'
 //
 template <typename GeometryTraits_2, typename TopologyTraits,
           typename InputIterator>
@@ -463,7 +463,7 @@ void insert(Arrangement_on_surface_2<GeometryTraits_2, TopologyTraits>& arr,
 //
 // error: no matching function for call to `do_intersect(Arrangement_2<>&,
 // const Arr_segment_2&, const Arr_walk_along_line_point_location<>&,
-// mpl_::bool_< true>)'
+// std::bool_constant< true>)'
 //
 template <typename GeometryTraits_2, typename TopologyTraits,
           typename InputIterator>
@@ -1524,7 +1524,7 @@ zone(Arrangement_on_surface_2<GeometryTraits_2, TopologyTraits>& arr,
 // workaround since it didn't compile in FC3_g++-3.4.4 with the error of:
 //
 // error: no matching function for call to `do_intersect(Arrangement_on_surface_2<>&,
-// const Arr_segment_2&, const Arr_walk_along_line_point_location<>&, mpl_::bool_< true>)'
+// const Arr_segment_2&, const Arr_walk_along_line_point_location<>&, std::bool_constant< true>)'
 //
 template <typename GeometryTraits_2, typename TopologyTraits,
           typename PointLocation>
@@ -1562,7 +1562,7 @@ do_intersect(Arrangement_on_surface_2<GeometryTraits_2, TopologyTraits>& arr,
 //
 // error: no matching function for call to
 // `do_intersect(Arrangement_on_surface_2<>&,
-// const Arr_segment_2&, const Arr_walk_along_line_point_location<>&, mpl_::bool_< true>)'
+// const Arr_segment_2&, const Arr_walk_along_line_point_location<>&, std::bool_constant< true>)'
 //
 template <typename GeometryTraits_2, typename TopologyTraits,
           typename PointLocation>
diff --git a/Arrangement_on_surface_2/include/CGAL/Surface_sweep_2/Arr_overlay_ss_visitor.h b/Arrangement_on_surface_2/include/CGAL/Surface_sweep_2/Arr_overlay_ss_visitor.h
index 30c8b38b4a0..06052a8f19d 100644
--- a/Arrangement_on_surface_2/include/CGAL/Surface_sweep_2/Arr_overlay_ss_visitor.h
+++ b/Arrangement_on_surface_2/include/CGAL/Surface_sweep_2/Arr_overlay_ss_visitor.h
@@ -295,7 +295,7 @@ protected:
    * \param tag The tag used for dispatching.
    */
   void _map_boundary_vertices(Event* event, Vertex_handle v,
-                              boost::mpl::bool_<true> /* tag */);
+                              std::bool_constant<true> /* tag */);
 
   /*!
    * Update the boundary vertices map.
@@ -306,7 +306,7 @@ protected:
    * \param tag The tag used for dispatching.
    */
   void _map_boundary_vertices(Event* event, Vertex_handle v,
-                              boost::mpl::bool_<false> /* tag */);
+                              std::bool_constant<false> /* tag */);
 
   /*!
    * Update a newly created vertex using the overlay traits.
@@ -319,7 +319,7 @@ protected:
    * \param tag The tag used for dispatching.
    */
   void _create_vertex(Event* event, Vertex_handle res_v, Subcurve* sc,
-                      boost::mpl::bool_<true> /* tag */);
+                      std::bool_constant<true> /* tag */);
 
   /*!
    * Update a newly created vertex using the overlay traits.
@@ -331,7 +331,7 @@ protected:
    * \param tag The tag used for dispatching.
    */
   void _create_vertex(Event* event, Vertex_handle res_v, Subcurve* sc,
-                      boost::mpl::bool_<false> /* tag */);
+                      std::bool_constant<false> /* tag */);
 
   /*!
    * Update a newly created edge using the overlay traits.
@@ -922,7 +922,7 @@ _map_halfedge_and_twin(Halfedge_handle he,
 //
 template <typename OvlHlpr, typename OvlTr, typename Vis>
 void Arr_overlay_ss_visitor<OvlHlpr, OvlTr, Vis>::
-_map_boundary_vertices(Event* event, Vertex_handle v, boost::mpl::bool_<true>)
+_map_boundary_vertices(Event* event, Vertex_handle v, std::bool_constant<true>)
 {
   // Update the red and blue object if the last event on sc is on the boundary.
   if ((event->parameter_space_in_x() != ARR_INTERIOR) ||
@@ -960,7 +960,7 @@ _map_boundary_vertices(Event* event, Vertex_handle v, boost::mpl::bool_<true>)
 template <typename OvlHlpr, typename OvlTr, typename Vis>
 void Arr_overlay_ss_visitor<OvlHlpr, OvlTr, Vis>::
 _map_boundary_vertices(Event* /* event */, Vertex_handle /* v */,
-                       boost::mpl::bool_<false>)
+                       std::bool_constant<false>)
 {}
 
 /* Notify the overlay traits about a newly created vertex.
@@ -974,7 +974,7 @@ void Arr_overlay_ss_visitor<OvlHlpr, OvlTr, Vis>::
 _create_vertex(Event* event,
                Vertex_handle new_v,
                Subcurve* sc,
-               boost::mpl::bool_<true>)
+               std::bool_constant<true>)
 {
   const Point_2& pt = event->point();
   const Cell_handle_red* red_handle = pt.red_cell_handle();
@@ -1011,7 +1011,7 @@ _create_vertex(Event* event,
     return;
   }
 
-  _create_vertex(event, new_v, sc, boost::mpl::bool_<false>());
+  _create_vertex(event, new_v, sc, std::bool_constant<false>());
 }
 
 /* Notify the overlay traits about a newly created vertex. */
@@ -1020,7 +1020,7 @@ void Arr_overlay_ss_visitor<OvlHlpr, OvlTr, Vis>::
 _create_vertex(Event* event,
                Vertex_handle new_v,
                Subcurve* sc,
-               boost::mpl::bool_<false>)
+               std::bool_constant<false>)
 {
   const Point_2& pt = event->point();
   const Cell_handle_red* red_handle = pt.red_cell_handle();
diff --git a/Arrangement_on_surface_2/test/Arrangement_on_surface_2/utils.h b/Arrangement_on_surface_2/test/Arrangement_on_surface_2/utils.h
index f49b92f4c01..f4975fb1428 100644
--- a/Arrangement_on_surface_2/test/Arrangement_on_surface_2/utils.h
+++ b/Arrangement_on_surface_2/test/Arrangement_on_surface_2/utils.h
@@ -55,13 +55,13 @@ private:
   // This function is invoked for traits classes where at least one
   // boundary is not oblivious and all boundaries are not identified.
   bool operator()(const Point_2& p1, const Point_2& p2,
-                  boost::mpl::bool_<false>) const
+                  std::bool_constant<false>) const
   { return (m_traits.compare_xy_2_object()(p1, p2) == CGAL::SMALLER); }
 
   // This function should be invoked for traits classes where at least one
   // boundary is identified.
   bool operator()(const Point_2& p1, const Point_2& p2,
-                  boost::mpl::bool_<true>) const
+                  std::bool_constant<true>) const
   {
     // Compare in y boundaries:
     CGAL::Arr_parameter_space ps_y1 =
diff --git a/BGL/include/CGAL/boost/graph/named_params_helper.h b/BGL/include/CGAL/boost/graph/named_params_helper.h
index 4dce0049b1a..7dd7edd0887 100644
--- a/BGL/include/CGAL/boost/graph/named_params_helper.h
+++ b/BGL/include/CGAL/boost/graph/named_params_helper.h
@@ -46,9 +46,9 @@ public:
                              typename boost::property_map<PolygonMesh, PropertyTag>::type,
                              typename boost::cgal_no_property::type> type;
   typedef std::conditional_t<Has_internal_pmap::value,
-                                    typename boost::property_map<PolygonMesh, PropertyTag>::const_type,
-                                    typename boost::cgal_no_property::const_type
-                                    >::type const_type;
+                             typename boost::property_map<PolygonMesh, PropertyTag>::const_type,
+                             typename boost::cgal_no_property::const_type
+                             > const_type;
 
   type get_pmap(const PropertyTag& p, PolygonMesh& pmesh)
   {
diff --git a/BGL/include/CGAL/boost/graph/properties.h b/BGL/include/CGAL/boost/graph/properties.h
index 1fd71599ad1..e8ab8b8bc43 100644
--- a/BGL/include/CGAL/boost/graph/properties.h
+++ b/BGL/include/CGAL/boost/graph/properties.h
@@ -140,7 +140,7 @@ struct Point_accessor<Handle, ValueType, ConstReference, true>
   typedef ValueType                      value_type;
   typedef Handle                         key_type;
 
-  typedef std::conditional_t< std::is_reference<ConstReference>,
+  typedef std::conditional_t< std::is_reference_v<ConstReference>,
                               ValueType&,
                               ValueType > Reference;
 
diff --git a/Number_types/include/CGAL/Sqrt_extension/Algebraic_structure_traits.h b/Number_types/include/CGAL/Sqrt_extension/Algebraic_structure_traits.h
index b1500148b59..c2175bc9439 100644
--- a/Number_types/include/CGAL/Sqrt_extension/Algebraic_structure_traits.h
+++ b/Number_types/include/CGAL/Sqrt_extension/Algebraic_structure_traits.h
@@ -206,7 +206,7 @@ public:
     // Tag_true if COEFF and ROOT are exact
     typedef std::conditional_t<
        std::is_same_v<typename CGAL::Algebraic_structure_traits<ROOT_ >::Is_exact,::CGAL::Tag_true> &&
-       std::is_same<typename CGAL::Algebraic_structure_traits<COEFF_>::Is_exact,::CGAL::Tag_true>
+       std::is_same_v<typename CGAL::Algebraic_structure_traits<COEFF_>::Is_exact,::CGAL::Tag_true>
            ,::CGAL::Tag_true,::CGAL::Tag_false> Is_exact;
 
     typedef typename Algebraic_structure_traits<COEFF_>::Is_numerical_sensitive
diff --git a/STL_Extension/include/CGAL/Concurrent_compact_container.h b/STL_Extension/include/CGAL/Concurrent_compact_container.h
index e6a2a5dbecf..7f5533f92b7 100644
--- a/STL_Extension/include/CGAL/Concurrent_compact_container.h
+++ b/STL_Extension/include/CGAL/Concurrent_compact_container.h
@@ -1,4 +1,4 @@
-3// Copyright (c) 2012  INRIA Sophia-Antipolis (France).
+// Copyright (c) 2012  INRIA Sophia-Antipolis (France).
 // All rights reserved.
 //
 // This file is part of CGAL (www.cgal.org)
diff --git a/STL_Extension/include/CGAL/Container_helper.h b/STL_Extension/include/CGAL/Container_helper.h
index aeb66ea052b..9f5ac5a84cb 100644
--- a/STL_Extension/include/CGAL/Container_helper.h
+++ b/STL_Extension/include/CGAL/Container_helper.h
@@ -50,8 +50,8 @@ void resize(Container& CGAL_assertion_code(array), std::size_t CGAL_assertion_co
 template <class Container>
 void resize(Container&, std::size_t,
             std::enable_if_t<
-              !boost::mpl::or_<has_resize<Container>,
-                               has_size<Container> >::value >* = nullptr)
+              !(has_resize<Container>::value ||
+                has_size<Container>::value)>* = nullptr)
 {
 }
 
diff --git a/Triangulation_2/include/CGAL/Constrained_triangulation_2.h b/Triangulation_2/include/CGAL/Constrained_triangulation_2.h
index 02b050f790a..3cc57168971 100644
--- a/Triangulation_2/include/CGAL/Constrained_triangulation_2.h
+++ b/Triangulation_2/include/CGAL/Constrained_triangulation_2.h
@@ -95,9 +95,10 @@ namespace internal {
 
 template <typename K>
 struct Itag {
-  typedef std::conditional_t<(typename Algebraic_structure_traits<typename K::FT>::Is_exact)::value,
-                                   Exact_intersections_tag,
-                                   Exact_predicates_tag> type;
+  using Is_exact = typename Algebraic_structure_traits<typename K::FT>::Is_exact;
+  typedef std::conditional_t<Is_exact::value,
+                             Exact_intersections_tag,
+                             Exact_predicates_tag> type;
 };
 
 } // namespace internal