We propose to study the properties of magnetic (multilayer) films using the recently discovered technique of Magnetization induced Second Harmonic Generation. This nonlinear Magneto-Optical Kerr Effect (MOKE) is not only interface specific, but shows giant (103 x) enhancements relative to its linear counterpart. Magnetic multilayers show exciting new properties like Giant Magneto Resistance and oscillating exchange coupling, that have a great potential for practical applications. For these systems, the interfaces between the various metallic films play an essential role. Unfortunately, these buried interfaces are experimentally very hard to investigate by standard magnetic probes. By comparing nonlinear (interface) and linear (bulk) MOKE signals, we will be able to discriminate between bulk and interface contributions to the magnetic properties of thin multilayer films. This will shed new light on the important role of the interfaces for magnetic multilayer films.