Open source software has tremendous potential for improving the productivity of research labs and enabling the development of new medical applications. The Image-Guided Surgery Toolkit (IGSTK) is an open source software toolkit based on ITK, VTK, and FLTK, and uses the cross-platform tools CMAKE and DART to support common operating systems such as Linux, Windows, and MacOS. IGSTK integrates the basic components needed in surgical guidance applications and provides a common platform for fast prototyping and development of robust image-guided applications. This paper gives an overview of the IGSTK framework and current status of development followed by an example needle biopsy application to demonstrate how to develop an image-guided application using this toolkit.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.