  There is a strong connection between the formation of a disk galaxy and the
properties of the interstellar medium (ISM). Theoretical work has typically
either focused on the cosmological buildup of a galaxy with a relatively crude
model for the gas physics, or examined local processes in the ISM and ignored
the global evolution of the galaxy itself. Here, I briefly review what has been
learned from both of these approaches, and what can be done to bridge the gap
between them. I argue that cosmological simulations need to learn from
observational and theoretical work on local ISM properties and adopt more
sophisticated models for the processes that they cannot resolve. Since the ISM
is still incompletely understood, there are a number of reasonable approaches
for these "subgrid" models, and I will discuss the strengths and limitations of
each.
