  The magnetic field of molecular clouds (MCs) plays an important role in the
process of star formation: it determins the statistical properties of
supersonic turbulence that controls the fragmentation of MCs, controls the
angular momentum transport during the protostellar collapse, and affects the
stability of circumstellar disks. In this work, we focus on the problem of the
determination of the magnetic field strength. We review the idea that the MC
turbulence is super-Alfv\'{e}nic, and we argue that MCs are bound to be born
super-Alfv\'{e}nic. We show that this scenario is supported by results from a
recent simulation of supernova-driven turbulence on a scale of 250 pc, where
the turbulent cascade is resolved on a wide range of scales, including the
interior of MCs.
