  Star formation is inefficient. Recent advances in numerical simulations and
theoretical models of molecular clouds show that the combined effects of
interstellar turbulence, magnetic fields and stellar feedback can explain the
low efficiency of star formation. The star formation rate is highly sensitive
to the driving mode of the turbulence. Solenoidal driving may be more important
in the Central Molecular Zone, compared to more compressive driving agents in
spiral-am clouds. Both theoretical and observational efforts are underway to
determine the dominant driving mode of turbulence in different Galactic
environments. New observations with ALMA, combined with other instruments such
as CARMA, JCMT and the SMA begin to reveal the magnetic field structure of
dense cores and protostellar disks, showing highly complex field geometries
with ordered and turbulent field components. Such complex magnetic fields can
give rise to a range of stellar masses and jet/outflow efficiencies in dense
cores and protostellar accretion disks.
