Improving our understanding of the earliest stages of star formation is
crucial to gain insight into the origin of stellar masses, multiple systems,
and protoplanetary disks. We discuss recent advances made in this area thanks
to detailed mapping observations at infrared and (sub)millimeter wavelengths.
Although ambipolar diffusion appears to be too slow to play a direct role in
the formation of dense cores, there is nevertheless good evidence that the
gravitational collapse of isolated protostellar cores is strongly magnetically
controlled. We also argue that the beginning of protostellar collapse is much
more violent in cluster-forming clouds than in regions of distributed star
formation.Comment: 10 pages, 4 figures, to appear in the proceedings of the JENAM2003
minisymposium "Early Stages of Star Formation" (special issue of Baltic
Astronomy - M. Kun & J. Eisloeffel Eds.