I will argue that observations of the diffuse gas in the outskirts of 
galaxies, the so called circumgalactic medium, are essential for 
constraining the 'initial conditions' for galaxy formation. Such 
observations provide a fruitful comparison to theory, because 
hydrodynamics at moderate overdensities is much easier to simulate 
than molecule or star-formation.  A novel technique will be 
introduced, whereby a foreground quasar (and massive galaxy) can be 
studied in absorption against a background quasar, resolving scales as 
small as 30kpc. This experiment reveals a rich absorption spectrum 
which contains a wealth of information about the physical conditions 
of diffuse gas around massive proto-galaxies. I will summarize the 
implications of these new measurements in the context of galaxy 
formation models, and discuss the possibility of detecting cooling 
radiation in emission from the gas we study in absorption.