  This review summarizes the argument for molecular clouds being dominated by
turbulence, most likely super-Alfvenic turbulence. Five lines of observational
evidence are given: molecular linewidths and line shapes, nonequilibrium
chemical abundances, fractal cloud shapes, measurements of the dispersion of
dust extinction through clouds, and Zeeman measurements of the field strength.
Recent models by Padoan & Nordlund are summarized, that show that
super-Alfvenic turbulence appears consistent with these observations. I then
present recent computations of my own, with numerical resolution as high as
256^3 zones, confirming the basic picture proposed by Padoan & Nordlund, but
showing that the decay timescales they quote are actually too long. My
computations show that decaying turbulence loses its kinetic energy with a ~1/t
dependence on time regardless of whether the turbulence is subsonic,
supersonic, isothermal, adiabatic, unmagnetized or magnetized. Finally, the
implications for star formation and turbulence theory are discussed.
