  Star clusters form in dense, hierarchically collapsing gas clouds. Bulk
kinetic energy is transformed to turbulence with stars forming from cores fed
by filaments. In the most compact regions, stellar feedback is least effective
in removing the gas and stars may form very efficiently. These are also the
regions where, in high-mass clusters, ejecta from some kind of high-mass stars
are effectively captured during the formation phase of some of the low mass
stars and effectively channeled into the latter to form multiple populations.
Star formation epochs in star clusters are generally set by gas flows that
determine the abundance of gas in the cluster. We argue that there is likely
only one star formation epoch after which clusters remain essentially clear of
gas by cluster winds. Collisional dynamics is important in this phase leading
to core collapse, expansion and eventual dispersion of every cluster. We review
recent developments in the field with a focus on theoretical work.
