  We present the results of the five mid-IR 15 microns (12-18 microns LW3 band)
ISOCAM Guaranteed Time Extragalactic Surveys performed in the regions of the
Lockman Hole and Marano Field. The roughly 1000 sources detected, 600 of which
have a flux above the 80 % completeness limit, guarantee a very high
statistical significance for the integral and differential source counts from
0.1 mJy up to 5 mJy. By adding the ISOCAM surveys of the HDF-North and South
(plus flanking fields) and the lensing cluster A2390 at low fluxes and IRAS at
high fluxes, we cover four decades in flux from 50 microJy to 0.3 Jy. The slope
of the differential counts is very steep (alpha =-3.0) in the flux range 0.4-4
mJy, hence much above the Euclidean expectation of alpha =-2.5. When compared
with no-evolution models based on IRAS, our counts show a factor of 10 excess
at 400 microJy, and a fast convergence, with alpha =-1.6 at lower fluxes.
