The hot intergalactic medium seen in many groups preserves a record
of elements ejected by group galaxies during their evolution, and its
structure appears to have been modified by the poorly understood
"feedback" processes which limit the cooling of baryons in the Universe. 
In this talk, I will discuss how a study of the properties of galaxy 
groups, and comparisons between observations and cosmological simulations,
can be used to advance our understanding of feedback.