This guide to commissioning evaluation services complements the NSW Government Evaluation Framework and Toolkit. It promotes a proactive, planned and structured approach to commissioning evaluations, including information on when and how to commission an evaluation and how to make the most of the results. The guide draws on the principles and processes described in the Framework and Toolkit, but it is framed specifically in relation to the health context, and it focuses on commissioning an external evaluator. The guide may be used to assist NSW Health staff in developing a complete evaluation plan, or in drafting an evaluation plan to which a contracted evaluator can add value.