SUMMARYFusion legislation is the latest in a long line of reforms in mental health law that have sought to increase patient autonomy. It has not been without controversy, having been proposed and rejected in various jurisdictions throughout the UK and internationally, while causing considerable debate in the academic literature. This article considers some of the history and debate, along with the criminal justice provisions of the first piece of fusion legislation internationally, the Mental Capacity Act (Northern Ireland) 2016, and their potential implications.LEARNING OBJECTIVES•Understand the history of fusion legislation in the UK and internationally•Understand the advantages and disadvantages of fusion legislation•Understand the Mental Capacity Act (Northern Ireland) 2016 criminal justice provisionsDECLARATION OF INTERESTNone.