Heterogeneous photocatalysis is a promising technique for the abatement of organic and inorganic pollutants. This method is based on particular properties of semiconductor materials that irradiated with light of suitable energy (i.e. equal or higher than that of the band gap) can promote electrons from the valence to the conduction band with the contemporary generation of positive holes in the valence band. These photo-generated pairs can induce red-ox reactions. Heterogeneous photocatalytic reactions should be studied by following the same methodology used for heterogeneous catalytic reactions and similar problems must be faced. Photocatalytic oxidation has been recently the subject of numerous investigations aimed to reduce the amounts of organic pollutants in wastewaters. Membrane separation processes and photocatalytic ones can work successfully in tandem and a synergy has been recently demonstrated. Indeed, the membrane would play both the role of support for the photocatalyst and of selective barrier for the molecules to be degraded, thus realizing a very powerful system. This chapter reports fundamentals of both techniques, a method to determine the optical properties of the photocatalysts and some cases studies of the coupled photocatalysis-membrane systems.