diff --git a/cmake/modules/boards.cmake b/cmake/modules/boards.cmake
index c9c86030693..77f61c32f7b 100644
--- a/cmake/modules/boards.cmake
+++ b/cmake/modules/boards.cmake
@@ -5,7 +5,9 @@
 # Validate board and setup boards target.
 #
 # This CMake module will validate the BOARD argument as well as splitting the
-# BOARD argument into <BOARD> and <BOARD_REVISION>.
+# BOARD argument into <BOARD> and <BOARD_REVISION>. When BOARD_EXTENSIONS option
+# is enabled (default) this module will also take care of finding board
+# extension directories.
 #
 # If a board implementation is not found for the specified board an error will
 # be raised and list of valid boards will be printed.
@@ -19,11 +21,13 @@
 # Outcome:
 # The following variables will be defined when this CMake module completes:
 #
-# - BOARD:          Board, without revision field.
-# - BOARD_REVISION: Board revision
-# - BOARD_DIR:      Board directory with the implementation for selected board
-# - ARCH_DIR:       Arch dir for extracted from selected board
-# - BOARD_ROOT:     BOARD_ROOT with ZEPHYR_BASE appended
+# - BOARD:                Board, without revision field.
+# - BOARD_REVISION:       Board revision
+# - BOARD_DIR:            Board directory with the implementation for selected board
+# - ARCH_DIR:             Arch dir for extracted from selected board
+# - BOARD_ROOT:           BOARD_ROOT with ZEPHYR_BASE appended
+# - BOARD_EXTENSION_DIRS: List of board extension directories (If
+#                         BOARD_EXTENSIONS is not explicitly disabled)
 #
 # The following targets will be defined when this CMake module completes:
 # - board: when invoked, a list of valid boards will be printed
@@ -164,3 +168,21 @@ if(NOT BOARD_DIR)
 endif()
 
 add_custom_target(boards ${list_boards_commands} USES_TERMINAL)
+
+# Board extensions are enabled by default
+set(BOARD_EXTENSIONS ON CACHE BOOL "Support board extensions")
+zephyr_get(BOARD_EXTENSIONS)
+
+# Process board extensions
+if(BOARD_EXTENSIONS)
+  get_filename_component(board_dir_name ${BOARD_DIR} NAME)
+
+  foreach(root ${BOARD_ROOT})
+    set(board_extension_dir ${root}/boards/extensions/${board_dir_name})
+    if(NOT EXISTS ${board_extension_dir})
+      continue()
+    endif()
+
+    list(APPEND BOARD_EXTENSION_DIRS ${board_extension_dir})
+  endforeach()
+endif()
diff --git a/cmake/modules/dts.cmake b/cmake/modules/dts.cmake
index e21d9ead887..8236195ff85 100644
--- a/cmake/modules/dts.cmake
+++ b/cmake/modules/dts.cmake
@@ -150,8 +150,11 @@ endif()
 # with them.
 #
 
+zephyr_file(CONF_FILES ${BOARD_EXTENSION_DIRS} DTS board_extension_dts_files)
+
 set(dts_files
   ${DTS_SOURCE}
+  ${board_extension_dts_files}
   ${shield_dts_files}
   )
 
diff --git a/cmake/modules/kconfig.cmake b/cmake/modules/kconfig.cmake
index 9e4a6320b4c..7c4a059b570 100644
--- a/cmake/modules/kconfig.cmake
+++ b/cmake/modules/kconfig.cmake
@@ -84,6 +84,7 @@ if(EXTRA_CONF_FILE)
   string(REPLACE " " ";" EXTRA_CONF_FILE_AS_LIST "${EXTRA_CONF_FILE_EXPANDED}")
 endif()
 
+zephyr_file(CONF_FILES ${BOARD_EXTENSION_DIRS} KCONF board_extension_conf_files)
 
 # DTS_ROOT_BINDINGS is a semicolon separated list, this causes
 # problems when invoking kconfig_target since semicolon is a special
@@ -252,6 +253,7 @@ set(
   merge_config_files
   ${BOARD_DEFCONFIG}
   ${BOARD_REVISION_CONFIG}
+  ${board_extension_conf_files}
   ${CONF_FILE_AS_LIST}
   ${shield_conf_files}
   ${EXTRA_CONF_FILE_AS_LIST}
diff --git a/doc/hardware/porting/board_porting.rst b/doc/hardware/porting/board_porting.rst
index 00709215920..8482eacc726 100644
--- a/doc/hardware/porting/board_porting.rst
+++ b/doc/hardware/porting/board_porting.rst
@@ -242,6 +242,37 @@ followed by trial and error. If you want to understand details, you will need
 to read the rest of the devicetree documentation and the devicetree
 specification.
 
+Board extensions
+****************
+
+Board extensions are board fragments that can be present in a board root
+folder, under ``${BOARD_ROOT}/boards/extensions``. The extension folder must
+follow the naming structure of the original board to extend. The board extension
+directory may contain Kconfig fragments and/or devicetree overlays. Board
+extensions are, by default, automatically loaded and applied on top of board
+files, before anything else. There is no guarantee on which order extensions are
+applied, in case multiple exist. This feature shall be disabled by passing
+``-DBOARD_EXTENSIONS=OFF`` when building.
+
+Board extensions are designed for downstream users, for example,
+``example-application`` or vendor SDKs. In some situations, certain hardware
+description or `choices <devicetree-chosen-nodes>`_ can not be added in the
+upstream Zephyr repository, but they can be in a downstream project, where
+custom bindings or driver classes can also be created. This feature may also be
+useful in development phases, when the board skeleton lives upstream, but other
+features are developed in a downstream module.
+
+Note that board extensions need to follow the
+:ref:`same guidelines <porting-general-recommendations>` as regular boards. For
+example, it is wrong to enable extra peripherals or subsystems in a board
+extension.
+
+.. warning::
+
+   Board extensions are not allowed in any module referenced in Zephyr's
+   ``west.yml`` manifest file. Any board changes are required to be submitted to
+   the main Zephyr repository.
+
 .. _dt_k6x_example:
 
 Example: FRDM-K64F and Hexiwear K64