Complexity in transition metal oxides

A vast array of experimental and theoretical results in manganites has shown that the colossal magnetoresistance effect can be understood based on the competition of insulating and ferromagnetic phases. The general aspects of the theoretical description appear to be valid for any compound with intrinsic phase competition. In high temperature superconductors, recent experiments have shown the existence of intrinsic inhomogeneities in many materials, revealing a phenomenology quite similar to that of manganese oxides. We will review briefly the results for manganites in order to propose a similar scenario in the high Tc cuprates.