Lime (calcium oxide or calcium hydroxide) is arguably the most common reagent used in the extractive minerals processing industry. As an effective and economic pH modifier, lime is widely used in the process of selective flotation of the major sulphide minerals. This paper reviews: lime preparation factors that influence the reagent performance properties; mechanisms of lime interaction with collector chemicals and mineral surfaces; its role in promoting selective separation between different sulphide minerals; and the effect on pulp and froth properties. The practical aspects of lime dose locations and the most common sulphide flotation process applications are also discussed.