diff --git a/.gitignore b/.gitignore
index 2ac8abc..0ca1fcf 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,3 +2,4 @@
 /install*
 /.gradle
 /gradleDir
+toolchain
\ No newline at end of file
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 8f592cc..7233696 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -7,6 +7,40 @@ set(CMAKE_OSX_ARCHITECTURES arm64 x86_64)
 set(CMAKE_MSVC_DEBUG_INFORMATION_FORMAT Embedded)
 project(thirdparty-gtsam)
 
+include(FetchContent)
+
+# Fetch Eigen
+set(EIGEN_BUILD_BLAS OFF)
+set(EIGEN_BUILD_LAPACK OFF)
+fetchcontent_declare(
+    Eigen3
+    GIT_REPOSITORY    https://gitlab.com/libeigen/eigen.git
+    GIT_TAG           0fb2ed140d4fc0108553ecfb25f2d7fc1a9319a1
+    GIT_PROGRESS TRUE
+)
+FetchContent_GetProperties(Eigen3)
+
+if(NOT Eigen3_POPULATED)
+    FetchContent_Populate(Eigen3)
+
+    # Create a build directory for Eigen
+    set(eigen3_BUILD_DIR ${CMAKE_BINARY_DIR}/eigen3-build)
+    message("Eigen source is ${eigen3_SOURCE_DIR}, build is ${eigen3_BUILD_DIR}")
+    file(MAKE_DIRECTORY ${eigen3_BUILD_DIR})
+
+    # Configure Eigen
+    message("Hi configure - ${CMAKE_COMMAND} -S ${eigen3_SOURCE_DIR} -B ${eigen3_BUILD_DIR} -DCMAKE_INSTALL_PREFIX=${CMAKE_BINARY_DIR}/eigen-install")
+    execute_process(COMMAND ${CMAKE_COMMAND} -S ${eigen3_SOURCE_DIR} -B ${eigen3_BUILD_DIR} -DCMAKE_INSTALL_PREFIX=${CMAKE_BINARY_DIR}/eigen-install)
+
+    # Build and install Eigen
+    message("Hi install")
+    execute_process(COMMAND ${CMAKE_COMMAND} --build ${EIGEN_BUILD_DIR} --target install)
+    message("bye install")
+endif()
+
+# Set Eigen3_DIR to the installation location
+set(Eigen3_DIR ${CMAKE_BINARY_DIR}/eigen-install/share/eigen3/cmake)
+
 set(GTSAM_COMPILE_OPTIONS_PRIVATE_DEBUG CACHE INTERNAL FORCE)
 set(GTSAM_COMPILE_OPTIONS_PRIVATE_RELWITHDEBINFO CACHE INTERNAL FORCE)
 set(GTSAM_ENABLE_BOOST_SERIALIZATION OFF)
@@ -18,11 +52,12 @@ set(GTSAM_BUILD_TESTS OFF)
 set(BUILD_SHARED_LIBS OFF)
 set(GTSAM_FORCE_SHARED_LIB OFF)
 set(GTSAM_FORCE_STATIC_LIB ON)
+set(GTSAM_USE_SYSTEM_EIGEN ON)
 
-include(FetchContent)
 fetchcontent_declare(
     gtsam
-    GIT_REPOSITORY    https://github.com/mcm001/gtsam
-    GIT_TAG           c24ca7951f1db4cfe4e23f368b2eda503de72176
+    GIT_REPOSITORY    https://github.com/calcmogul/gtsam
+    GIT_TAG           79960095b9d8e03dd9ee83d7e0c9cab810a05a72
+    GIT_PROGRESS TRUE
 )
 fetchcontent_makeavailable(gtsam)
diff --git a/README.md b/README.md
index b49d7e3..2c9cd55 100644
--- a/README.md
+++ b/README.md
@@ -1,2 +1,6 @@
 # Third party gtsam
 Third party gradle packaging for gtsam
+
+## Updating thirdparty library version
+
+Eigen is now a submodule here that we ask GTSAM to pull in using GTSAM_USE_SYSTEM_EIGEN. Change the submodule SHA to update Eigen.