Key Performance Indicators are used increasingly by health services, but their relevance and utility may be questionable. In this article, Program Theory is used to model the irreducible stages in the system of clinical care in Child and Adolescent Mental Health Services, define the major program operations in each of these stages, and specify the intermediate outcomes of each stage and the final outcomes sought. National and State policy standards are used, with practice experience, to identify key program operations and intermediate outcomes sought. Systematic criteria are then applied to select KPIs that are measurable, reliable, valid for our program theory, utilitarian, and relevant to clinicians, clients and managers.