This Clinical Guideline addresses the evidence base for the theory and practice of Art Psychotherapy for clients who have severe and complex problems. It draws on different types of evidence – from users, experienced practitioners, local custom and practice, research and other related literature. It addresses both in-patient and community care, and situates the profession and its practices in the context of National Service Frameworks. The document begins with description of Art Psychotherapists’ long-standing history of work with this client population and, in so doing, outlines something of the development of the discipline’s theory and clinical practice. It describes the Guideline’s development, the aims and objectives of the project and the overall scope of the guideline. The processes of generating evidence through consultation with two expert panels – one comprising Art Psychotherapists experienced in this area of work and another comprising service users – are also described. The identification and critical appraisal of research and other texts relevant to the Guideline’s topic, and the development of evidence weightings appropriate to the discipline, are also explained. The Guideline then moves on to an extensive Evidence Review. This narrative describes the evidence the Guideline Development Group gleaned from all possible sources - textual, oral and practical. This includes research-based literature, other academically rigorous and descriptive literature and the opinions of expert practitioners, local practitioners and local expert users. The findings from the review process are described in the narrative and each is assigned to an evidence level. The evidence is reviewed thematically, for example regarding the contexts and settings of Art Psychotherapy practice, the referral process, assessment and clinical approaches. The theory that underpins clinical work is described first, followed by practice itself; the former (theory) derives almost entirely from the literature, but the latter (practice) is significantly informed by the opinions of our two expert panels and by the custom and practice of Art psychotherapists at Oxleas NHS Foundation Trust. In so doing, the Guideline addresses some of the gaps in the current Art Psychotherapy literature. The Evidence Review is followed by Recommendations. These distil the findings of the Review into General Principles and specific Recommendations for Art Psychotherapy practice with users who are prone to psychotic states. Each Principle and Recommendation is accompanied by a brief statement that refers to the evidence it has been derived from; like the evidence in the review, it too is assigned to a level. The highest level (1a and 1b) should be afforded the most significance. The document concludes with discussion of the implementation of the guideline and audit criteria.