Purpose: To review evidence describing how health and social care professionals in England and Wales assess mental capacity, in order to identify ways to improve practice.Methods: A systematised literature review was completed. Electronic databases of published medical, health and social care research and gray literature were searched. Journal articles and research reports published between 2007 and 2018 were included if they met predefined eligibility criteria. Evidence from included studies was synthesized using thematic analysis.Results: 20 studies of variable methodological quality were included. The studies described assessments carried out by a range of multidisciplinary professionals working with different groups of service users in diverse care contexts. Four main themes were identified: preparation for assessment; capacity assessment processes; supported decision-making; interventions to facilitate or improve practice. There was a lack of detailed information describing how professionals provided information to service users and tested their decision-making abilities. Practice reported in studies varied in terms of its conformity to legal requirements.Conclusions: This review synthesized evidence about mental capacity assessment methods and quality in England and Wales and analyzed it to suggest ways in which practice might be improved.Implications for rehabilitationMental capacity assessment practice in England and Wales varies and is not always consistent with legal requirements, risking inconsistent and inaccurate judgements about capacity and exposure to legal action.Interventions have been developed to help professionals to engage in supported decision-making, and improve their mental capacity assessments and documentation in line with legal standards.These interventions include training and practical resources, such as assessment flowcharts, checklists and documentation aids. Such interventions would benefit from robust evaluation before they are implemented more widely.