The vtkSystemIncludes centralizes the inclusion of system include files. (This is particularly important as VTK moves towards ANSI C++.) For example, this include file enables user's to build VTK with STL (i.e., use std::ostream and other standard ANSI C++ functionality). A compile-time flag (VTK_USE_ANSI_STDLIB) must be set to enable ANSI C++ compliance. You'll probably also need to set various compiler flags. For example, on WIndows for ANSI C++, use /D "VTK_USE_ANSI_STDLIB" /GX /Zm1000 .