I'm trying to include the Eigen library in my Xcode Project.

I've copied the "Eigen" folder, which contains all of the necessary header files, into my Xcode Projects.
I've added the path to this folder to my Xcode Project's Header Search Paths.
This folder is set to *not* search recursively.

When I attempt to build this project, I see a lot of errors around the Block.h file, and my Xcode project cannot build.
I have tried this on both the LLVM and GCC compilers.

I have the following error notificaitons:
/Eigen/src/Core/Block.h:50:21: 'XprType' does not refer to a value
/Eigen/src/Core/Block.h:50:15: Use of undeclared identifier 'Block'; did you mean 'clock'?
/Eigen/src/Core/Block.h:50:8: Explicit specialization of non-template struct 'traits'
/Eigen/src/Core/Block.h:50:64: Expected unqualified-id
/Eigen/src/Core/Block.h:96:42: Use of undeclared identifier 'Dynamic'
/Eigen/src/Core/Block.h:97:43: No member named 'has_direct_access' in namespace 'Eigen::internal'
/Eigen/src/Core/Block.h:97:61: 'XprType' does not refer to a value
/Eigen/src/Core/Block.h:97:71: No type named 'ret' in the global namespace
/Eigen/src/Core/Block.h:97:74: Expected unqualified-id
/Eigen/src/Core/Block.h:104:90: Expected '>'
/Eigen/src/Core/Block.h:104:90: Expected class name
/Eigen/src/Core/Block.h:106:91: Expected '>'
/Eigen/src/Core/Block.h:106:91: Expected member name or ';' after declaration specifiers
/Eigen/src/Core/Block.h:109:13: Unknown type name 'Impl'
/Eigen/src/Core/Block.h:110:5: Unknown type name 'EIGEN_GENERIC_PUBLIC_INTERFACE'
/Eigen/src/Core/Block.h:110:42: Expected ';' at end of declaration list
/Eigen/src/Core/Block.h:149:60: Use of undeclared identifier 'Dense'
/Eigen/src/Core/Block.h:167:22: Unknown template name 'dense_xpr_base'
Too many errors emitted, stopping now

So does Eigen just not build in Xcode at all? I was under the impression that this could just work?

Eigen works perfectly fine with XCode. Can you show the #include statements of your .cpp that fails to compile?