  Interstellar turbulence is expected to dissipate quickly in the absence of
continuous energy input. I examine the energy available for driving the
turbulence from six likely mechanisms: magnetorotational instability,
gravitational instability, protostellar outflows, H II region expansion,
stellar winds, and supernovae. I conclude that supernovae contribute far more
energy than the other mechanisms, and so form the most likely drving mechanism.
