This report, written by Constitution Unit Deputy Director Dr Alan Renwick and published jointly by the Constitution Unit and the UCL European Institute, sets out what we can say now about how the process of Brexit will unfold. It begins by providing an overview of the negotiations, including what form any deal might take, whether the time available for reaching a deal might be extended, and whether the UK, if it wants, can revoke the triggering of Article 50. It then examines the possible roles and behaviours of each of the key actors in turn. It argues that it will be very difficult for the government to deliver the ambitious package set out by Theresa May in her Lancaster House speech on 17 January 2017 within the two-year timeframe that she envisages. There are several possible ways in which the Brexit process might instead resolve itself.