Abstract
In this talk we present a review of the observational difficulties for the determination of the Initial Mass Function (IMF) and make a summary of the observational data that can be used to constrain the IMF. We also show how well the proposed effective IMF and other popular IMFs fit some of these constraints. In this short contribution we point out a series of effects that must be taken into account to recover the high mass IMF from the observed Present Day Mass Function (PDMF).
