DataViewer (see Figure) is a scientific visualization library created to allow the easy development of efficient visualization programs for those who are not graphics programming experts. It consists of a high-level set of routines for rendering geometric objects and utilizes the OpenGL graphics API for its low level rendering. DataViewer has been used for several different visualization tasks, e.g. most of VBM's visualization modules have been developed using it. The goals that have driven the design of DataViewer are to be efficient, easy to use, portable, closely connectable to numerical computations, and available free of charge to the mathematical and scientific community.