Treatment manuals are important in replicating treatments, but despite their increased use in corrections, little attention has been paid to what makes a good offender treatment programme manual. A Delphi survey of an international sample of 32 offender treatment programme trainers was conducted to determine the features of a good treatment manual. The Delphi survey, which allows experts to share their opinions anonymously, involved three rounds of participation, with 32, 20, and 14 completing Rounds 1, 2 and 3, respectively. Features considered to be of importance in a manual were: a comprehensible account of the programme theory, clearly stated aims and objectives, detailed instructions, advice on delivery, examples and choices, readable presentation, jargon-free language, and user-friendly format of materials.