  Simulations from the scales of isolated galaxies to clouds have been
instrumental in informing us about molecular cloud formation and evolution.
Simulations are able to investigate the roles of gravity, feedback, turbulence,
heating and cooling, and magnetic fields on the physics of the interstellar
medium, and star formation. Compared to simulations of individual clouds,
galactic and sub-galactic scale simulations can include larger galactic scale
processes such as spiral arms, bars, and larger supernovae bubbles, which may
influence star formation. Simulations show cloud properties and lifetimes in
broad agreement with observations. Gravity and spiral arms are required to
produce more massive GMCs, whilst stellar feedback, likely photoionisation,
leads to relatively short cloud lifetimes. On larger scales, supernovae may be
more dominant in driving the structure and dynamics, but photoionisation may
still have a role. In terms of the dynamics, feedback is probably the main
driver of velocity dispersions, but large scale processes such as gravity and
spiral arms may also be significant. Magnetic fields are generally found to
decrease star formation on galaxy or cloud scales, and simulations are ongoing
to study whether clouds are sub or supercritical on different scales in galaxy
scale simulations. Simulations on subgalactic scales, or zoom in simulations,
allow better resolution of feedback processes, filamentary structure within
clouds, and the study of stellar clusters.
