  The origin of the lowest mass free-floating objects -- brown dwarfs and
planetary-mass objects -- is one of the major unsolved problems in star
formation. Establishing a census of young substellar objects is a fundamental
prerequisite for distinguishing between competing theoretical scenarios. Such a
census allows us to probe the initial mass function (IMF), binary statistics,
and properties of accretion disks. Our SONYC (Substellar Objects in Nearby
Young Clusters) survey relies on extremely deep wide-field optical and
near-infrared imaging, with follow-up spectroscopy, in combination with Spitzer
photometry to probe the bottom end of the IMF to unprecedented levels. Here we
present SONYC results for three different regions: NGC 1333, rho Ophiuchus and
Chamaeleon-I. In NGC 1333, we find evidence for a possible cutoff in the mass
function at 10-20 Jupiter masses. In rho Oph we report a new brown dwarf with a
mass close to the deuterium-burning limit.
