  We present results from an ISOCAM survey in the two broad band filters LW2
(5-8.5 mu) and LW3 (12-18 mu) of a 0.13 square degree coverage of the Serpens
Main Cloud Core. A total of 392 sources were detected in the 6.7 mu band and
139 in the 14.3 mu band to a limiting sensitivity of ~ 2 mJy. Only about 50% of
the mid-IR excess sources show excesses in the near-IR J-H/H-K diagram. In the
central Cloud Core the Class I/Class II number ratio is 19/18, i.e. about 10
times larger than in other young embedded clusters such as rho Ophiuchi or
Chamaeleon. The mid-IR fluxes of the Class I and flat-spectrum sources are
found to be on the average larger than those of Class II sources. Stellar
luminosities are estimated for the Class II sample, and its luminosity function
is compatible with a coeval population of about 2 Myr which follows a three
segment power-law IMF. For this age about 20% of the Class IIs are found to be
young brown dwarf candidates. The YSOs are in general strongly clustered, the
Class I sources more than the Class II sources, and there is an indication of
sub-clustering. The sub-clustering of the protostar candidates has a spatial
scale of 0.12 pc. These sub-clusters are found along the NW-SE oriented ridge
and in very good agreement with the location of dense cores traced by
millimeter data. The smallest clustering scale for the Class II sources is
about 0.25 pc, similar to what was found for rho Ophiuchi. Our data show
evidence that star formation in Serpens has proceeded in several phases, and
that a ``microburst'' of star formation has taken place very recently, probably
within the last 10^5 yrs.
