diff --git a/CMakeLists.txt b/CMakeLists.txt
index 230dfe3b67..f6da045f8e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -205,51 +205,47 @@ endif()
 # Do OSX checks
 include(cmake/MacOSX.cmake)
 
-# Check if we are using 2019 intel compilers or gcc 6.1 or 6.2 together with pybind11, and forbid the use of C++17 if so.
+# Check if we are using 2019 intel compilers or gcc 6.1 or 6.2 together with pybind11, and forbid the use of C++17 or later if so.
+set(PERMIT_CXX17_PLUS_CHECK TRUE)
 if(HAVE_PYBIND11)
   if(("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Intel" AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER 18.0.6) OR
      ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU" AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER 5.6 AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 6.3))
-    set(PERMIT_CXX17_CHECK FALSE)
-  else()
-    set(PERMIT_CXX17_CHECK TRUE)
+    set(PERMIT_CXX17_PLUS_CHECK FALSE)
   endif()
 endif()
 
-# Prevent using C++17 if using gnu version 7.2
+# Prevent using C++17 or later if using gnu version 7.2
 if("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU" AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER 7.1 AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 7.3)
-    set(PERMIT_CXX17_CHECK FALSE)
+    set(PERMIT_CXX17_PLUS_CHECK FALSE)
 endif()
 
-# Check for C++11, C++14 and C++17 support.
+# GAMBIT requires at least C++17. Use the newest standard the compiler supports, up to C++23.
 include(CheckCXXCompilerFlag)
-if(PERMIT_CXX17_CHECK)
-  CHECK_CXX_COMPILER_FLAG("-std=c++17" COMPILER_SUPPORTS_CXX17)
+if(PERMIT_CXX17_PLUS_CHECK)
+  CHECK_CXX_COMPILER_FLAG("-std=c++23" COMPILER_SUPPORTS_CXX23)
 endif()
-if(COMPILER_SUPPORTS_CXX17)
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++17")
-  set(GAMBIT_SUPPORTS_CXX17 TRUE)
+if(COMPILER_SUPPORTS_CXX23)
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++23")
+  set(GAMBIT_SUPPORTS_CXX23 TRUE)
 else()
-  if(PERMIT_CXX17_CHECK)
-    CHECK_CXX_COMPILER_FLAG("-std=c++1z" COMPILER_SUPPORTS_CXX1z)
+  if(PERMIT_CXX17_PLUS_CHECK)
+    CHECK_CXX_COMPILER_FLAG("-std=c++20" COMPILER_SUPPORTS_CXX20)
   endif()
-  CHECK_CXX_COMPILER_FLAG("-std=c++14" COMPILER_SUPPORTS_CXX14)
-  if(COMPILER_SUPPORTS_CXX14)
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++14")
-    set(GAMBIT_SUPPORTS_CXX14 TRUE)
+  if(COMPILER_SUPPORTS_CXX20)
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++20")
+    set(GAMBIT_SUPPORTS_CXX20 TRUE)
   else()
-    CHECK_CXX_COMPILER_FLAG("-std=c++1y" COMPILER_SUPPORTS_CXX1y)
-    CHECK_CXX_COMPILER_FLAG("-std=c++11" COMPILER_SUPPORTS_CXX11)
-    if(COMPILER_SUPPORTS_CXX11)
-      set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
-      set(GAMBIT_SUPPORTS_CXX11 TRUE)
+    if(PERMIT_CXX17_PLUS_CHECK)
+      CHECK_CXX_COMPILER_FLAG("-std=c++17" COMPILER_SUPPORTS_CXX17)
+    endif()
+    if(COMPILER_SUPPORTS_CXX17)
+      set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++17")
+      set(GAMBIT_SUPPORTS_CXX17 TRUE)
     else()
-      CHECK_CXX_COMPILER_FLAG("-std=c++0x" COMPILER_SUPPORTS_CXX0X)
-      if(COMPILER_SUPPORTS_CXX0X)
-        set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++0x")
-        set(GAMBIT_SUPPORTS_CXX0X TRUE)
-      else()
-        message(FATAL_ERROR "The compiler ${CMAKE_CXX_COMPILER} has no C++11 support. Please use a different C++ compiler.")
-      endif()
+      message(FATAL_ERROR "${BoldRed}The compiler ${CMAKE_CXX_COMPILER} does not support C++17. GAMBIT requires a "
+                          "compiler with at least C++17 support. Please use a newer compiler, or if a known "
+                          "pybind11/compiler incompatibility is blocking the check above, retry with "
+                          "-DWITH_PYBIND11=OFF.${ColourReset}")
     endif()
   endif()
 endif()
@@ -321,12 +317,15 @@ if("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang" OR "${CMAKE_CXX_COMPILER_ID}" STR
 endif()
 
 # Check for Eigen
-find_package(Eigen3 3.1.0)
+# Note: a minimum of 3.3.7 (rather than the older 3.1.0) is required because Eigen releases
+# prior to that use several STL idioms (std::unary_function/std::binary_function, std::result_of,
+# etc.) in their own headers that are deprecated or removed under C++17/C++20/C++23.
+find_package(Eigen3 3.3.7)
 if(EIGEN3_FOUND)
   include_directories(SYSTEM "${EIGEN3_INCLUDE_DIR}")
   message("-- Eigen version: ${EIGEN3_VERSION}")
 else()
-  message("${BoldRed}   Eigen v3.1.0 or greater not found.  FlexibleSUSY and GM2Calc interfaces will be excluded.${ColourReset}")
+  message("${BoldRed}   Eigen v3.3.7 or greater not found.  FlexibleSUSY and GM2Calc interfaces will be excluded.${ColourReset}")
   set(itch "${itch};gm2calc;flexiblesusy")
   message(FATAL_ERROR "\nFlexibleSUSY is currently included in the GAMBIT distribution, so in fact it cannot be ditched.  Please install Eigen3.\nIf Eigen3 is already installed in a non-standard location, you can point CMake to it by passing -DEIGEN3_INCLUDE_DIR=/path/to/eigen on the command line, or by setting the environment variable EIGEN3_ROOT (or EIGEN3_ROOT_DIR).\n(Note that this will change in future GAMBIT versions, where FlexibleSUSY will be a 'true' backend.)")
 endif()
diff --git a/ColliderBit/include/gambit/ColliderBit/colliders/Pythia8/Py8Collider.hpp b/ColliderBit/include/gambit/ColliderBit/colliders/Pythia8/Py8Collider.hpp
index be21d480ed..17505e1db3 100644
--- a/ColliderBit/include/gambit/ColliderBit/colliders/Pythia8/Py8Collider.hpp
+++ b/ColliderBit/include/gambit/ColliderBit/colliders/Pythia8/Py8Collider.hpp
@@ -62,7 +62,7 @@ namespace Gambit
         /// An exception for when Pythia fails to initialize.
         class InitializationError : public std::exception
         {
-          virtual const char* what() const throw()
+          virtual const char* what() const noexcept
           {
             return "Pythia could not initialize.";
           }
@@ -70,7 +70,7 @@ namespace Gambit
         /// An exception for when Pythia fails to generate events.
         class EventGenerationError : public std::exception
         {
-          virtual const char* what() const throw()
+          virtual const char* what() const noexcept
           {
             return "Pythia could not make the next event.";
           }
diff --git a/Printers/include/gambit/Printers/printers/hdf5printer/hdf5_combine_tools.hpp b/Printers/include/gambit/Printers/printers/hdf5printer/hdf5_combine_tools.hpp
index 889f00414a..0f2a623190 100644
--- a/Printers/include/gambit/Printers/printers/hdf5printer/hdf5_combine_tools.hpp
+++ b/Printers/include/gambit/Printers/printers/hdf5printer/hdf5_combine_tools.hpp
@@ -210,7 +210,7 @@ namespace Gambit
                 template <typename U>
                 static void run (U, hid_t &dataset_out, hid_t &dataset2_out, std::vector<hid_t> &datasets, std::vector<hid_t> &datasets2, const unsigned long long size, const std::unordered_map<PPIDpair, unsigned long long, PPIDHash, PPIDEqual>& RA_write_hash, const std::vector<std::vector <unsigned long long> > &pointid, const std::vector<std::vector <unsigned long long> > &rank, const std::vector<unsigned long long> &aux_sizes, hid_t &/*old_dataset*/, hid_t &/*old_dataset2*/)
                 {
-                    std::vector<U> output(size, 0);
+                    std::vector<U> output(size);
                     std::vector<int> valids(size, 0);
 
                     // Should no longer need the old datasets, they should have already been copied during "copy_hdf5"
diff --git a/Utils/include/gambit/Utils/exceptions.hpp b/Utils/include/gambit/Utils/exceptions.hpp
index 2e05a40ca1..80aa37f726 100644
--- a/Utils/include/gambit/Utils/exceptions.hpp
+++ b/Utils/include/gambit/Utils/exceptions.hpp
@@ -64,13 +64,13 @@ namespace Gambit
       /// @}
 
       /// Destructor
-      virtual ~exception() throw() {}
+      virtual ~exception() noexcept {}
 
       /// Setter for the fatal flag.
       void set_fatal(bool);
 
       /// Retrieve the identity of the exception.
-      virtual const char* what() const throw();
+      virtual const char* what() const noexcept;
 
       /// Raise the exception.
       /// Log the exception and, if it is considered fatal, actually throw it.
@@ -199,10 +199,10 @@ namespace Gambit
       special_exception(const char*);
 
       /// Destructor
-      virtual ~special_exception() throw() {}
+      virtual ~special_exception() noexcept {}
 
       /// Retrieve the identity of the exception.
-      virtual const char* what() const throw();
+      virtual const char* what() const noexcept;
 
       /// Retrieve the message that this exception was raised with.
       std::string message();
@@ -338,7 +338,7 @@ namespace Gambit
     public:
       SilentShutdownException();
       SilentShutdownException(const std::string& message);
-      virtual const char* what() const throw();
+      virtual const char* what() const noexcept;
     private:
       std::string myWhat;
   };
@@ -347,7 +347,7 @@ namespace Gambit
   {
     public:
       SoftShutdownException(const std::string& message);
-      virtual const char* what() const throw();
+      virtual const char* what() const noexcept;
     private:
       std::string myWhat;
   };
@@ -356,7 +356,7 @@ namespace Gambit
   {
     public:
       HardShutdownException(const std::string& message);
-      virtual const char* what() const throw();
+      virtual const char* what() const noexcept;
     private:
       std::string myWhat;
   };
@@ -365,7 +365,7 @@ namespace Gambit
   {
     public:
       MPIShutdownException(const std::string& message);
-      virtual const char* what() const throw();
+      virtual const char* what() const noexcept;
     private:
       std::string myWhat;
   };
diff --git a/Utils/include/gambit/Utils/util_types.hpp b/Utils/include/gambit/Utils/util_types.hpp
index b35cd4ed76..5cefeb30d8 100644
--- a/Utils/include/gambit/Utils/util_types.hpp
+++ b/Utils/include/gambit/Utils/util_types.hpp
@@ -365,7 +365,7 @@ namespace Gambit
       typedef calc_nElem<lims... > nElem;
       T array[nElem::val];
       Farray(){}
-      Farray(Farray<T,lims... > &in){*this = in;}
+      Farray(const Farray<T,lims... > &in){*this = in;}
       template <typename ... Args>
       typename enable_if_all_member<allowed_types, T&, Args...>::type::type
       operator () (Args ... a)
diff --git a/Utils/src/exceptions.cpp b/Utils/src/exceptions.cpp
index 0f6073b600..ff74e61cbf 100644
--- a/Utils/src/exceptions.cpp
+++ b/Utils/src/exceptions.cpp
@@ -183,7 +183,7 @@ namespace Gambit
     }
 
     /// Retrieve the identity of the exception.
-    const char* exception::what() const throw()
+    const char* exception::what() const noexcept
     {
       return myWhat.c_str();
     }
@@ -365,7 +365,7 @@ namespace Gambit
     special_exception::special_exception(const char* what) : myWhat(what), myMessage("") {}
 
     /// Retrieve the identity of the exception.
-    const char* special_exception::what() const throw()
+    const char* special_exception::what() const noexcept
     {
       const char* temp;
       temp = myWhat;
@@ -524,22 +524,22 @@ namespace Gambit
     /// @{ SilentShutdownException member functions
     SilentShutdownException::SilentShutdownException() {}
     SilentShutdownException::SilentShutdownException(const std::string& message) : myWhat(message) {}
-    const char* SilentShutdownException::what() const throw() { return myWhat.c_str(); }
+    const char* SilentShutdownException::what() const noexcept { return myWhat.c_str(); }
     /// @}
 
     /// @{ SoftShutdownException member functions
     SoftShutdownException::SoftShutdownException(const std::string& message) : myWhat(message) {}
-    const char* SoftShutdownException::what() const throw() { return myWhat.c_str(); }
+    const char* SoftShutdownException::what() const noexcept { return myWhat.c_str(); }
     /// @}
 
     /// @{ HardShutdownException member functions
     HardShutdownException::HardShutdownException(const std::string& message) : myWhat(message) {}
-    const char* HardShutdownException::what() const throw() { return myWhat.c_str(); }
+    const char* HardShutdownException::what() const noexcept { return myWhat.c_str(); }
     /// @}
 
     /// @{ MPIShutdownException member functions
     MPIShutdownException::MPIShutdownException(const std::string& message) : myWhat(message) {}
-    const char* MPIShutdownException::what() const throw() { return myWhat.c_str(); }
+    const char* MPIShutdownException::what() const noexcept { return myWhat.c_str(); }
     /// @}
 
     /// Global instance of piped invalid point class.
diff --git a/cmake/backends.cmake b/cmake/backends.cmake
index 2f827fe5f5..9c2baaae0d 100644
--- a/cmake/backends.cmake
+++ b/cmake/backends.cmake
@@ -1716,10 +1716,9 @@ set(patch "${PROJECT_SOURCE_DIR}/Backends/patches/${name}/${ver}/patch_${name}")
 # - Silence the deprecated-declarations warnings coming from Eigen3
 set(GM2CALC_CXX_FLAGS "${BACKEND_CXX_FLAGS}")
 set_compiler_warning("no-deprecated-declarations" GM2CALC_CXX_FLAGS)
-# - gm2calc 1.2 depends on std::ptr_fun which is removed in c++17, so we need to fall back to c++14 (or c++11)
-if(COMPILER_SUPPORTS_CXX17)
-  string(REGEX REPLACE "-std=c\\+\\+17" "-std=c++14" GM2CALC_CXX_FLAGS "${GM2CALC_CXX_FLAGS}")
-endif()
+# - gm2calc 1.2 depends on std::ptr_fun, which was removed in C++17, so we need to fall back to
+#   C++14 regardless of which (C++17 or later) standard GAMBIT itself is using.
+string(REGEX REPLACE "-std=c\\+\\+(17|1z|20|2a|23|2b)" "-std=c++14" GM2CALC_CXX_FLAGS "${GM2CALC_CXX_FLAGS}")
 set(GM2CALC_MAKESHAREDLIB "${CMAKE_CXX_COMPILER} ${CMAKE_SHARED_LINKER_FLAGS} ${NO_FIXUP_CHAINS} ${CMAKE_SHARED_LIBRARY_CREATE_CXX_FLAGS}")
 check_ditch_status(${name} ${ver} ${dir})
 if(NOT ditched_${name}_${ver})
@@ -1747,10 +1746,9 @@ set(patch "${PROJECT_SOURCE_DIR}/Backends/patches/${name}/${ver}/patch_${name}")
 # - Silence the deprecated-declarations warnings coming from Eigen3
 set(GM2CALC_CXX_FLAGS "${BACKEND_CXX_FLAGS}")
 set_compiler_warning("no-deprecated-declarations" GM2CALC_CXX_FLAGS)
-# - gm2calc 1.3 depends on std::ptr_fun which is removed in c++17, so we need to fall back to c++14 (or c++11)
-if(COMPILER_SUPPORTS_CXX17)
-  string(REGEX REPLACE "-std=c\\+\\+17" "-std=c++14" GM2CALC_CXX_FLAGS "${GM2CALC_CXX_FLAGS}")
-endif()
+# - gm2calc 1.3 depends on std::ptr_fun, which was removed in C++17, so we need to fall back to
+#   C++14 regardless of which (C++17 or later) standard GAMBIT itself is using.
+string(REGEX REPLACE "-std=c\\+\\+(17|1z|20|2a|23|2b)" "-std=c++14" GM2CALC_CXX_FLAGS "${GM2CALC_CXX_FLAGS}")
 set(GM2CALC_MAKESHAREDLIB "${CMAKE_CXX_COMPILER} ${CMAKE_SHARED_LINKER_FLAGS} ${NO_FIXUP_CHAINS} ${CMAKE_SHARED_LIBRARY_CREATE_CXX_FLAGS}")
 check_ditch_status(${name} ${ver} ${dir})
 if(NOT ditched_${name}_${ver})
@@ -2102,9 +2100,10 @@ set(dir "${PROJECT_SOURCE_DIR}/Backends/installed/${name}/${ver}")
 # OpenMP flags don't play nicely with clang and FastJet's antiquated libtoolized build system.
 string(REGEX REPLACE "-Xclang -fopenmp" "" FJ_C_FLAGS "${BACKEND_C_FLAGS}")
 string(REGEX REPLACE "-Xclang -fopenmp" "" FJ_CXX_FLAGS "${BACKEND_CXX_FLAGS}")
-# FastJet 3.3.2 depends on std::auto_ptr which is removed in c++17, so we need to fall back to c++14 (or c++11)
-string(REGEX REPLACE "-std=c\\+\\+17" "-std=c++14" FJ_CXX_FLAGS "${FJ_CXX_FLAGS}")
-string(REGEX REPLACE "-std=c\\+\\+17" "-std=c++14" FJ_C_FLAGS "${FJ_C_FLAGS}")
+# FastJet 3.3.2 depends on std::auto_ptr, which was removed in C++17, so we need to fall back to
+# C++14 regardless of which (C++17 or later) standard GAMBIT itself is using.
+string(REGEX REPLACE "-std=c\\+\\+(17|1z|20|2a|23|2b)" "-std=c++14" FJ_CXX_FLAGS "${FJ_CXX_FLAGS}")
+string(REGEX REPLACE "-std=c\\+\\+(17|1z|20|2a|23|2b)" "-std=c++14" FJ_C_FLAGS "${FJ_C_FLAGS}")
 set_compiler_warning("no-deprecated-declarations" FJ_CXX_FLAGS)
 set_compiler_warning("no-deprecated-copy" FJ_CXX_FLAGS)
 set(FJ_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} ${NO_FIXUP_CHAINS}")
diff --git a/cmake/cmake_variables.hpp.in b/cmake/cmake_variables.hpp.in
index 50264b7d0e..fb20d99851 100644
--- a/cmake/cmake_variables.hpp.in
+++ b/cmake/cmake_variables.hpp.in
@@ -46,12 +46,15 @@
 /// Name of the gambit executable
 #define GAMBIT_EXECUTABLE "@PROJECT_NAME@"
 
-/// Compiler supports C++14 features
-#cmakedefine COMPILER_SUPPORTS_CXX14 1
-
 /// Compiler supports C++17 features
 #cmakedefine COMPILER_SUPPORTS_CXX17 1
 
+/// Compiler supports C++20 features
+#cmakedefine COMPILER_SUPPORTS_CXX20 1
+
+/// Compiler supports C++23 features
+#cmakedefine COMPILER_SUPPORTS_CXX23 1
+
 /// Found link.h in system paths
 #cmakedefine HAVE_LINK_H 1
 
diff --git a/cmake/externals.cmake b/cmake/externals.cmake
index a6602e022e..d1f5eccb63 100644
--- a/cmake/externals.cmake
+++ b/cmake/externals.cmake
@@ -202,9 +202,6 @@ function(check_ditch_status name version dir)
       set (itch "${itch}" "${name}_${version}")
     elseif ((arg STREQUAL "x11") AND NOT X11_FOUND)
       set (itch "${itch}" "${name}_${version}")
-    elseif ((arg STREQUAL "c++14") AND NOT GAMBIT_SUPPORTS_CXX14 AND NOT GAMBIT_SUPPORTS_CXX17)
-      message("${BoldCyan} X ${name} (${version}) needs c++14/17 but GAMBIT is compiled with a lower version. ${name} will be excluded.${ColourReset}")
-      set (itch "${itch}" "${name}_${version}")
     elseif ((arg STREQUAL "rivet") AND ditched_rivet_${Rivet_ver})
       set (itch "${itch}" "${name}_${version}")
     endif()
diff --git a/cmake/optional.cmake b/cmake/optional.cmake
index 6ff3fb856c..45987beb02 100644
--- a/cmake/optional.cmake
+++ b/cmake/optional.cmake
@@ -211,9 +211,14 @@ if(NOT LAPACK_LINKLIBS AND NOT LAPACK_FOUND)
 endif()
 
 # Helper function to check if ROOT has been compiled with the same standard as we are using here.  If not, downgrade to the standard that ROOT was compiled with.
+# Note: only C++17 and later are matched here, so a ROOT installation built with an older
+# standard will not be matched and will trigger the "unable to detect" error below, prompting
+# the user to rebuild ROOT with at least C++17.
 function(check_root_std_flag)
-  # Loop over C++ standards
-  set(std_list "17;1z;14;1y;11;0x")
+  # Loop over C++ standards, newest first. "2b"/"2a"/"1z" are the pre-standardisation aliases
+  # that some compilers historically used for C++23/C++20/C++17 respectively, and are included
+  # here purely so that older ROOT builds using those flag spellings are still detected.
+  set(std_list "23;2b;20;2a;17;1z")
   foreach(std ${std_list})
     set(CXX_FLAG "-std=c++${std}")
     set(CXX_FLAG_RE "-std=c\\+\\+${std}")
@@ -257,7 +262,8 @@ function(check_root_std_flag)
   # Did we figure out the std used by ROOT?
   if(NOT ROOT_USES_STD)
     message(FATAL_ERROR "${BoldRed}Unable to detect what flavour of C++ your installation of ROOT has "
-                        "been compiled with; please set -DWITH_ROOT=OFF.${ColourReset}")
+                        "been compiled with, or it was compiled with an unsupported (pre-C++17) standard. "
+                        "Please rebuild ROOT with at least C++17, or set -DWITH_ROOT=OFF.${ColourReset}")
   endif()
   # Check that the std used by ROOT is OK
   CHECK_CXX_COMPILER_FLAG(${ROOT_CXX_FLAG} COMPILER_SUPPORTS_CXX${ROOT_STD})
diff --git a/cmake/warnings.cmake b/cmake/warnings.cmake
index 643c4d13b8..8e69c6f8ec 100644
--- a/cmake/warnings.cmake
+++ b/cmake/warnings.cmake
@@ -43,12 +43,6 @@ set_compiler_warning("all" CMAKE_CXX_FLAGS)
 set_compiler_warning("extra" CMAKE_CXX_FLAGS)
 set_compiler_warning("no-misleading-indentation" CMAKE_CXX_FLAGS)
 
-if(EIGEN3_FOUND AND EIGEN3_VERSION VERSION_LESS 3.3.0)
-  set_compiler_warning("no-ignored-attributes" CMAKE_CXX_FLAGS)
-  set_compiler_warning("no-deprecated-register" CMAKE_CXX_FLAGS)
-  set_compiler_warning("no-deprecated-declarations" CMAKE_CXX_FLAGS)
-endif()
-
 # set intel warnings
 if("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Intel")
   # "remark #981: operands are evaluated in unspecified order"
diff --git a/contrib/fjcore-3.2.0/fjcore.cc b/contrib/fjcore-3.2.0/fjcore.cc
index 85b5f611b3..9d833480ca 100644
--- a/contrib/fjcore-3.2.0/fjcore.cc
+++ b/contrib/fjcore-3.2.0/fjcore.cc
@@ -726,15 +726,19 @@ FJCORE_END_NAMESPACE
 FJCORE_BEGIN_NAMESPACE      // defined in fastjet/internal/base.hh
 class ClosestPair2D : public ClosestPair2DBase {
 public:
+  // GAMBIT: these constructors used to be defined inline here, but since Point is only
+  // forward-declared at this point in the class (and not fully defined until after
+  // ClosestPair2D's own class definition, below), their bodies -- which implicitly
+  // default-construct the std::vector<Point> _points member -- were being parsed in the
+  // "complete-class context" immediately after this class's closing brace, i.e. before
+  // Point was complete. Clang (unlike GCC) enforces this strictly under C++20/23, so the
+  // definitions are moved out-of-line, after Point is fully defined, matching the pattern
+  // already used below for _ID() and size().
   ClosestPair2D(const std::vector<Coord2D> & positions,
-		const Coord2D & left_corner, const Coord2D & right_corner) {
-    _initialize(positions, left_corner, right_corner, positions.size());
-  };
+		const Coord2D & left_corner, const Coord2D & right_corner);
   ClosestPair2D(const std::vector<Coord2D> & positions,
 		const Coord2D & left_corner, const Coord2D & right_corner,
-		const unsigned int max_size) {
-    _initialize(positions, left_corner, right_corner, max_size);
-  };
+		const unsigned int max_size);
   void closest_pair(unsigned int & ID1, unsigned int & ID2,
 		    double & distance2) const;
   void remove(unsigned int ID);
@@ -809,6 +813,15 @@ inline bool floor_ln2_less(unsigned x, unsigned y) {
   if (x>y) return false;
   return (x < (x^y)); // beware of operator precedence...
 }
+inline ClosestPair2D::ClosestPair2D(const std::vector<Coord2D> & positions,
+		const Coord2D & left_corner, const Coord2D & right_corner) {
+  _initialize(positions, left_corner, right_corner, positions.size());
+}
+inline ClosestPair2D::ClosestPair2D(const std::vector<Coord2D> & positions,
+		const Coord2D & left_corner, const Coord2D & right_corner,
+		const unsigned int max_size) {
+  _initialize(positions, left_corner, right_corner, max_size);
+}
 inline int ClosestPair2D::_ID(const Point * point) const {
   return point - &(_points[0]);
 }
diff --git a/contrib/yaml-cpp-0.6.2/include/yaml-cpp/node/detail/node_iterator.h b/contrib/yaml-cpp-0.6.2/include/yaml-cpp/node/detail/node_iterator.h
index 377e5a59b6..d025aa8519 100755
--- a/contrib/yaml-cpp-0.6.2/include/yaml-cpp/node/detail/node_iterator.h
+++ b/contrib/yaml-cpp-0.6.2/include/yaml-cpp/node/detail/node_iterator.h
@@ -57,11 +57,11 @@ struct node_iterator_type<const V> {
   typedef node_map::const_iterator map;
 };
 
+// GAMBIT: node_iterator_base used to derive from std::iterator<...> to pick up the standard
+// iterator typedefs, but that base class template was deprecated in C++17 and removed
+// altogether in C++20, so we provide the required typedefs directly instead.
 template <typename V>
-class node_iterator_base
-    : public std::iterator<std::forward_iterator_tag, node_iterator_value<V>,
-                           std::ptrdiff_t, node_iterator_value<V>*,
-                           node_iterator_value<V>> {
+class node_iterator_base {
  private:
   struct enabler {};
 
@@ -76,7 +76,11 @@ class node_iterator_base
  public:
   typedef typename node_iterator_type<V>::seq SeqIter;
   typedef typename node_iterator_type<V>::map MapIter;
+  typedef std::forward_iterator_tag iterator_category;
   typedef node_iterator_value<V> value_type;
+  typedef std::ptrdiff_t difference_type;
+  typedef node_iterator_value<V>* pointer;
+  typedef node_iterator_value<V> reference;
 
   node_iterator_base()
       : m_type(iterator_type::NoneType), m_seqIt(), m_mapIt(), m_mapEnd() {}
diff --git a/gum/CMakeLists.txt b/gum/CMakeLists.txt
index 1cc1687d05..568cf0f2f5 100644
--- a/gum/CMakeLists.txt
+++ b/gum/CMakeLists.txt
@@ -111,21 +111,22 @@ if(CMAKE_SYSTEM_PROCESSOR MATCHES "x86_64")
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fPIC")
 endif()
 
-# Check for C++11 and C++14 support
+# GUM requires at least C++17. Use the newest standard the compiler supports, up to C++23.
 include(CheckCXXCompilerFlag)
-CHECK_CXX_COMPILER_FLAG("-std=c++14" COMPILER_SUPPORTS_CXX14)
-if(COMPILER_SUPPORTS_CXX14)
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++14")
+CHECK_CXX_COMPILER_FLAG("-std=c++23" COMPILER_SUPPORTS_CXX23)
+if(COMPILER_SUPPORTS_CXX23)
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++23")
 else()
-  CHECK_CXX_COMPILER_FLAG("-std=c++11" COMPILER_SUPPORTS_CXX11)
-  if(COMPILER_SUPPORTS_CXX11)
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
+  CHECK_CXX_COMPILER_FLAG("-std=c++20" COMPILER_SUPPORTS_CXX20)
+  if(COMPILER_SUPPORTS_CXX20)
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++20")
   else()
-    CHECK_CXX_COMPILER_FLAG("-std=c++0x" COMPILER_SUPPORTS_CXX0X)
-    if(COMPILER_SUPPORTS_CXX0X)
-      set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++0x")
+    CHECK_CXX_COMPILER_FLAG("-std=c++17" COMPILER_SUPPORTS_CXX17)
+    if(COMPILER_SUPPORTS_CXX17)
+      set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++17")
     else()
-      message(FATAL_ERROR "The compiler ${CMAKE_CXX_COMPILER} has no C++11 support. Please use a different C++ compiler.")
+      message(FATAL_ERROR "The compiler ${CMAKE_CXX_COMPILER} does not support C++17. GUM requires a compiler "
+                          "with at least C++17 support. Please use a newer compiler.")
     endif()
   endif()
 endif()