Devolution was defined in 1999 by Professor Vernon Bogdanor as ‘the transfer to a subordinate body, on a geographical basis, of functions [at present] exercised by ministers and Parliament.’ Devolution has created devolved governments and legislatures that can enact laws and policies in specific areas (such as health, education, or transport), while Westminster retains sovereignty and control over ‘reserved’ matters (for instance defence and foreign affairs). The day-to-day operation of the devolution arrangement rests upon two largely unknown and rather opaque mechanisms: Joint Ministerial Committees, which are dedicated to solving potential public disagreement between the British and devolved governments, and Sewel conventions, which aim to ensure that the British Parliament would not normally legislate in devolved areas without the consent of the devolved parliaments. At the early stages of devolution, such mechanisms were scarcely used. They later became central elements of the devolution arrangement, until the Brexit referendum marked a steep decline in relations between Westminster and Holyrood. This paper will set out the constitutional framework in which Sewel conventions and Joint Ministerial Committees operate. It will explore how the status of Sewel conventions has evolved over the 25 years since devolution and what recent changes were made to Joint Ministerial Committees to improve their efficacy. It will take stock of the latest evolutions in these essential mechanisms which ensure a smooth functioning of the devolution process.