Most lubricants are manufactured from petroleum-based mineral oils; however, the use of environmentally friendly vegetable oil–based lubricants is growing. Mineral oils suffer from low viscosity indexes and vegetable oils suffer from high pour points. In this chapter viscosity index improvement for mineral oils and pour point depression for vegetable oils are discussed. It is concluded that polymethacrylates (PMAs) provide the best performance for viscosity index improvement in mineral oils, but olefin copolymers are utilized in larger quantities due to lower costs. Styrene-maleic anhydride copolymers (PSMAs) show the best performance as pour point depressants in vegetable oils, but due to lower costs, polymethacrylates are used in larger quantities. The use of polymethacrylates as viscosity index improvers is expected to increase as engine oils are required to perform over wider temperature ranges with developing engine technology. Modified versions of polymethacrylates and PSMAs, including star morphologies, and entirely new chemistries designed specifically for vegetable oils are needed to reach the desired level of pour point depression.