Surface and ultrathin‐film magnetocrystalline anisotropy in epitaxial fcc Fe thin films grown on room‐temperature Cu(100) single crystals has been investigated,insitu, by the combined surface magneto‐optical Kerr effects (SMOKE). In polar, longitudinal, and transverse Kerr effects, the direction of the applied magnetic field must be distinguished from the direction of magnetization during the switching process. For arbitrary orientations of the magnetization and field axis relative to the optical scattering plane, any of the three Kerr effects may contribute to the detected signal. A general expression for the normalized light intensity sensed by a photodiode detector, involving all three combined Kerr effects, is obtained both in the ultrathin‐film limit and for bulk, at general oblique incidence angles and with different orientations of the polarizer, modulator, and analyzer. This expression is used to interpret the results of fcc Fe/Cu(100) SMOKE measurements. For films grown at room temperature, polar and longitudinal Kerr‐effect magnetization loops show that the easy axis of magnetization rotates from the (canted) out‐of‐plane direction to the in‐plane direction at a thickness of about 4.7 monolayers. Transverse Kerr‐effect measurements indicate that the in‐plane easy axes are biaxial.