The catalytic effect of micelles, polymers (such as DNA, polypeptides) and nanoparticles, saturable receptors (cyclodextrins and calixarenes) and more complex systems (mixing some of the above mentioned catalysts) have been reviewed. In these microheterogeneous systems the observed changes in the rate constants have been rationalized using the Pseudophase Model. This model produces equations that can be derived from the Brönsted equation, which is the basis for a more general formulation of catalytic effects, including electrocatalysis. When, in the catalyzed reaction one of the reactants is in the excited state, the applicability (at least formally) of the Pseudophase Model occurs only in two limiting situations: the lifetime of the fluorophore and the distributions of the quencher and the probe are the main properties that define the different situations.