ISOCAM cosmological surveys

Several deep surveys have been performed at 7 and 15 mu m by using the mid- infrared camera ISOCAM on board the ISO satellite. We review their first re sults, emphasizing on the excess detected in the 15 mu m counts with respec t to the predictions of models with a mild evolution that is sufficient to explain the IRAS counts. We point out that a large fraction of the past sta r formation history is missed when studied using UV/visible data only.