FOGO (FOssil Group Origins) represent an ambitious project aimed at carrying out a systematic and comprehensive study of Fossil groups (FGs) using several facilities at La Palma Observatories, with time already allocated by the International Time Programme (ITP) during semesters 2008B, 2009A, 2009B, and 2010A.

FGs are systems with masses and X-ray haloes comparable to those of groups and clusters of galaxies, but whose optical light is dominated by a single, large elliptical galaxy surrounded by much fainter companions. Their denomination, fossil, comes from their possible formation scenario in which they may have collapsed at an early epoch. This early assembly leaves enough time for intermediate-luminosity galaxies to merge by dynamical friction and thus makes FGs the oldest and most relaxed galaxy systems.
The formation of the brightest group galaxy (BGG) through these intense merging events may result in large amounts of intra-group material, which could contribute up to 40% of  the groups total optical luminosity. However, in spite of this high merging efficiency, FGs may still pose a significant challenge  to structure formation theories, as they have been argued to posses two orders of magnitude less satellites than predicted by numerical simulations.