  Massive stars form in clusters within self-gravitating molecular clouds. The
size scale of these clusters is sufficiently large that non-thermal, or
turbulent, motions of the gas must be taken into account when considering their
formation. Millimeter wavelength radio observations of the gas and dust in
these clouds reveal a complex, self-similar structure that reflects the
turbulent nature of the gas. Differences are seen, however, towards dense bound
cores in proto-clusters. Examination of the kinematics of gas around such cores
suggests that dissipation of turbulence may be the first step in the star
formation process. Newly formed stars, on the other hand, replenish turbulence
through their winds and outflows. In this way, star formation may be
self-regulated. Observations and simulations are beginning to demonstrate the
key role that cloud turbulence plays in the formation and evolution of stellar
groups.
