  Turbulence, self-gravity, and cooling convert most of the interstellar medium
into cloudy structures that form stars. Turbulence compresses the gas into
clouds directly and it moves pre-existing clouds around passively when there
are multiple phases of temperature. Self-gravity also partitions the gas into
clouds, forming giant regular complexes in spiral arms and in resonance rings
and contributing to the scale-free motions generated by turbulence. Dense
clusters form in the most strongly self-gravitating cores of these clouds,
often triggered by compression from local stars. Pre-star formation processes
inside clusters are not well observed, but the high formation rates and high
densities of pre-stellar objects, and their power law mass functions suggest
that turbulence, self-gravity, and energy dissipation are involved there too.
