Firefly (previously known as the PC GAMESS) is a freely available ab initio and DFT computational chemistry program developed to offer high performance on Intel-compatible x86, AMD64, and EM64T processors. Firefly package is being developed by the Firefly Project Team. The project coordinator and leading developer is Dr. Alex A. Granovsky. A number of other researchers have made significant contributions to the project over last years, especially those of Drs. Anastasia V. Bochenkova and James W. Kress are to be mentioned. The project was launched in 1994. Initially, it was named ”the PC GAMESS” and was based on the GAMESS (US) source code of ISUQCG (versions of up to October 25, 1999), while extending its functionality in many important areas. However, since 1999, no part of the GAMESS (US) was incorporated into the PC GAMESS, nor will it be added in the future, as the development of the PC GAMESS (now Firefly) became completely independent of the GAMESS (US) development. Nevertheless, the high-level compatibility of input and output files between these two packages was enforced to as much extent as possible for different programs. However, until very recently (fall 2008), due to its historical roots, the package name was ”PC GAMESS”, and it was distributed as the part of GAMESS (US) distribution from the ISUQCG web site. As of Autumn 2008, the Firefly Project Team, as well as Firefly itself are no longer associated with GAMESS (US) and ISUQCG group. Starting December 4, 2009, the only valid name for the former PC GAMESS package is the ”Firefly” one.