GAP (Groups, Algorithms and Programming) is a computer algebra system for computational discrete algebra with particular emphasis on computational group theory.GAP was developed at Lehrstuhl D fr Mathematik (LDFM), RWTH Aachen, Germany from 1986 to 1997. After the retirement of J. Neubser from the chair of LDFM, the development and maintenance of GAP was coordinated by the School of Mathematical and Computational Sciences at the University of St Andrews, Scotland. In the summer of 2005 coordination was transferred to an equal partnership of four 'GAP Centres', located at the University of St Andrews; RWTH Aachen; the Technische Universitt Braunschweig; and Colorado State University at Fort Collins.GAP and its sources, including packages (sets of user contributed programs), data library (including a list of small groups) and the manual, are distributed freely, subject to "copyleft" conditions. GAP runs on any Unix system, under Windows, and on Macintosh systems. The standard distribution requires about 300 MB (about 400 MB if all the packages are loaded). To run GAP, 128 MB of RAM is sufficient.