NETGEN is an automatic 3d tetrahedral mesh generator with Python interface. It accepts input from constructive solid geometry (CSG) or boundary representation (BRep) from STL file format. The connection to a geometry kernel (OCCT) allows the handling of IGES and STEP files. NETGEN contains modules for mesh optimization and hierarchical mesh refinement. Open source, LGPL license; available for Linux, macOS and Windows.