Following its formal withdrawal from the EU on 31 January 2020 the UK entered into a 'Transition' period until 31 December 2020. During these 11 months EU law continued to apply in the UK. Transition was due to be used to prepare for the full implementation of the Protocol on Ireland/Northern Ireland. Both the UK and the EU published various key documents concerning implementation. The UK government also announced that it would not be availing of the opportunity to extend the Transition period

A first key document relating to the Protocol was a Technical Note on the implementation of the Protocol published by the European Commission on 20 April 2020.

This was followed by Command Paper setting out The UK's Approach to the Northern Ireland Protocol published by the UK Government on 20 May 2020. 

On 10 December 2020, following 'in principle' agreement with the EU on a number of outstanding issues concerning the implementation of the Protocol, the UK government published a second Command Paper on The Northern Ireland Protocol setting out its perspective on what had been agreed. A week later the EU-UK Joint Committee adopted the related Decisions.