  Stars and star clusters form by gravoturbulent fragmentation of interstellar
gas clouds. The supersonic turbulence ubiquitously observed in Galactic
molecular gas generates strong density fluctuations with gravity taking over in
the densest and most massive regions. Collapse sets in to build up stars.
Turbulence plays a dual role. On global scales it provides support, while at
the same time it can promote local collapse. Stellar birth is thus intimately
linked to the dynamical behavior of parental gas cloud, which governs when and
where protostars form, and how they contract and grow in mass via accretion
from the surrounding cloud material. The thermodynamic behavior of the star
forming gas plays a crucial part in this process and influences the stellar
mass function as well as the dynamic properties of the nascent stellar cluster.
This lecture provides a critical review of our current understand- ing of
stellar birth and compares observational data with competing theoretical
models.
