The basic concepts of photocatalysis are explored in this chapter. Various parameters which control and influence the photocatalytic process are studied in relation to the mechanistic approach. Metal oxides like titanium dioxide, zinc oxide, cerium oxide, tungsten oxide and bismuth oxides play an important role in photocatalysis for environmental remediation, water splitting and solar cells. The phenomenon of photocatalysis is dependent on wavelength of incident light. However, the efficiency of most of the metal oxides is limited in the UV range. It is needed to modify their band gap energy levels. These modifications can be achieved by doping or coupling of metals, non-metals, metal oxides and carbon based materials. Metal oxides morphologies also affect the photocatalytic process due to enhanced surface area and surface defects providing more accessible sites for the diffusion of organics. Some new types of materials like perovskite and metal organic framework (MOF) are used as efficient photocatalysts. The role and mechanism of these materials have been discussed. All these nanomaterials are used for the environmental remediation, dye sensitized solar cells, air purifications, hydrogen production and self-cleaning process.