Gammasphere is the world's premier high-resolution $\gamma $-ray detector facility for nuclear structure research and is a central component in a highly successful national and international nuclear structure program. It consists of 110 large volume, high purity germanium detectors, each in a BGO compton suppression shield. The device is especially powerful for collecting gamma ray data following heavy-ion reactions, when multiplicities can be high and Doppler shifts large. It has high granularity, which allows many gamma rays to be measured simultaneously, and permits precise correction for Doppler shifts. It has a photopeak efficiency for 1.3 MeV gamma-rays of 10%. As such, Gammasphere is the worlds most powerful spectrometer for nuclear structure research, rivalled only by Euroball.

The original concept for Gammasphere was proposed by Frank Stephens in 1987. This immediately led to formation of the Gammasphere Steering Committee comprising Frank Stephens (Chair), Doug Cline, Dave Fossan, Teng-Lek Khoo and I-Yang Lee. The Gammasphere Proposal was submitted in May 1988 and funded in 1991. Cline chaired the Gammasphere Steering Committee from 1989-1991. A consortium of scientists from national laboratories and many universities designed and built Gammasphere. The project was coordinated by scientists at Lawrence Berkeley National Laboratory under Frank Stephens leadership, culminating in its commissioning at LBNL in 1995. Gammasphere was located at the LBNL 88" Cyclotron from commissioning until 1997, and from 2000-2003. Gammasphere was sited at the Argonne National Laboratory ATLAS facility during 1998-1999 and since March 2003. Since commissioning the physics impact and productivity of Gammaspherehave been extraordinary, i.e. 584 journal publications and 99 Ph.D. theses as of July 2006. Highlights of the earliest phase of operation of Gammasphere are given in the Gammasphere On-line Booklet.