  My aim in this talk is to make clear that there are two sides to galaxy
formation: the properties of the galaxies themselves, and the properties of the
material that is left over from the galaxy formation process. To date, galaxy
formation studies have focused on correctly predicting the properties of
galaxies, and I will review the tremendous level of success in this area.
However, these models usually ignore the ``flip side'' of galaxy formation: the
intergalactic medium and the intra-group/intra-cluster medium (ICM). Yet,
Chandra and XMM have given us a good view of the ICM and their results present
an equally important challenge for theoretical models. I will show that this
challenge is far from easy to meet, but describe the Bower et al 2008 model of
galaxy formation which successfully combines both sides of the observational
constraints.
