planning and delivery of liaison psychiatry services requires many decisions regarding, for example, staffing profile; the type of work to be undertaken and by which members of the team; the relation between the team’s work and the work of other parts of the local mental health services; and how outcomes will be measured. Putting all these decisions together with the rationale for them amounts to what is sometimes called a programme theory or logic model for the service – outlining what is expected to work for whom and under what circumstances. These decisions are not made in isolation: key influences on the final shape of a service will depend upon the views (and financial support!) of service commissioners, which are in turn influenced by national policy. Even a carefully worked-out configuration for a liaison service is unlikely to be realised exactly as planned – implementation (delivery) will be influenced by the practical limitations experienced by staff in day-to-day work, and by the views of patients and of the health professionals who do (or do not) refer to the service.