There are insufficient resources available globally, nationally and in many regions, to conserve all species, habitats and ecosystems. Prioritisation of targets or actions is a rational response to resource scarcity. Prioritisation can be directed at areas for reservation, species, habitats or ecosystems for management, and threat management actions. The scale at which prioritisation is applied is a fundamental decision, and the range includes global, national, regional and patch. Choice of scale influences availability of data and methods available for prioritisation. Since 1986 availability of data, computing power and expertise available have all improved globally and in many countries. Approaches to prioritisation have evolved during the past 25 years as researchers from several disciplines, including biology, ecology, decision sciences, mathematics and economics, have sought ways to achieve greater output from the resources available for biodiversity conservation. This review surveys the literature and groups prioritisation approaches into the following four categories: reserves and reserve selection, prescriptive costed biodiversity prioritisation, ranked costed biodiversity projects and contracted costed conservation actions. A concluding section considers the limitations of current prioritisation approaches and points to areas for further development.