The GMT system was initiated in late 1987 at Lamont-Doherty Earth Observatory, Columbia University by graduate students Paul Wessel and Walter H. F. Smith. Version 1 was officially introduced to Lamont scientists in July 1988. GMT 1 migrated by word of mouth (and tape) to other institutions in the United States, UK, Japan, and France and attracted a small following. Paul took a Post-doctoral position at SOEST in December 1989 and continued the GMT development. Version 2.0 was released with an article in EOS, October 1991, and quickly spread worldwide. We obtained NSF-funding for GMT version 3.0 in 1993 which was released with another article in EOS on August 15, 1995. Significantly improved versions (3.1-3.3, 3.3.1-6), 3.4, 3.4.1-4, and 4.0 were released between November 1998 and October 2004, culminating in the January 2006 introduction of 4.1 (and service release 3.4.6). GMT now is used by 10,000 users worldwide in a broad range of disciplines.