The Visualization ToolKit (vtk) is a software system for 3D Computer Graphics and Visualization. Vtk includes a textbook published by Prentice-Hall ("The Visualization Toolkit, An Object-Oriented Approach To 3D Graphics, 2nd edition" ISBN 0-13-954694-4), a C++ class library, and several interpreted interface layers including Tcl/Tk, Java, and Python. Vtk has been implemented on nearly every Unix-based platform and PC's (Windows NT and Windows95). The design and implementation of the library has been strongly influenced by object-oriented principles.