Nanocomposites are multiphase materials that attracted considerable attention as very efficient photocatalytic materials. The nanocomposite photocatalysts contain semiconductors and metals as reinforced nanophase and photocatalytic activity is result of this heterojunction with matrix. The aim of this section is to explore some of the most representative nanocomposite materials with photocatalytic and electro-photocatalytic properties. These reactions are an alternative solution to use sunlight energy in degradation of contaminants from air and water, synthesis of new organic compounds, and as energy source. The reaction between photons and nanocomposite materials (powder, fiber, and film) is associated with generation of the reactive oxygen species that play a key role in these applications. The effects of heterojunctions between different semiconductors and metals and their considerable synergy that promote the photocatalytic properties of nanocomposites are evidenced. The mechanisms of various types of the photocatalytic reactions are thus presented highlighting the efficient strategy to suppress the recombination of e−/h+ pairs. The variation of the visible light absorption in the photocatalytic reaction and increasing of its efficiency, selectivity, and stability due the contribution of the surface plasmon resonance effect produced by precious metals nanoparticles is also considered.