Steam injection is widely used for heavy oil and bitumen recovery. The advantage of this process is its high recovery factor and its high oil production rate. However, the high production rate is associated with excessive energy consumption, carbon dioxide generation, and expensive post-production water treatment. Some of these disadvantages are overcome or reduced by the addition of solvent mixtures to steam. The steam-solvent processes are complex oil displacement methods involving simultaneous heat, mass, and fluid transport. These processes are not clearly understood despite their apparent importance to the oil industry. Systematic studies are essential in the design, analysis, and evaluation of the steam-solvent processes as well as in mathematical simulation. These studies provide valuable insights for petroleum engineers to improve the oil recovery efficiency when applied in a reservoir. Results of these processes are scattered in many publications over more than 40 years and are not readily available for most petroleum engineers. The purpose of the paper is to present a review of current knowledge and available data, and to delineate the steam-solvent processes.