The referendum concerning the UK's membership of the EU took place on June 23 2016, resulting in majority voting to leave the EU. This article traces developments in this area in six stages. It begins with an explanation of why the Prime Minister promised a referendum in 2013; this is followed by the significance of the balance of competence review conducted by the Coalition government; the focus then shifts to the PM's renegotiation with the EU after his electoral success in 2015; there is then discussion of the issues that shaped the referendum debate; the final two parts address respectively the political and legal fall-out from the referendum.