The countdown to Brexit has started. Given the short timeframe to Brexit and the large trading volumes, the authors investigate which certainties and uncertainties exist regarding the future trade relationship between the European Union (EU) and the United Kingdom (UK). Certain is that the UK is leaving the EU on 29 March 2019. On the basis of the recently presented draft withdrawal agreement, however, the chances are apparent that the UK will not leave the EU Customs Union and the internal market during a transition period ending in December 2020. Taking into account a possible transition period, the authors discuss the most likely scenarios and their impact on trade between the EU and the UK, in particular from a customs perspective.