The 1640s and 1650s saw the state assume an unprecedented predominance in the public life of Westminster. This chapter reveals for the first time how Westminster Abbey lay at the religious and ceremonial heart of the interregnum regimes, while its daughter church of St Margaret’s only began its special relationship with the House of Commons in these years. Not only is Westminster shown to have served as the daily ceremonial heart of government (both religious and secular), but it also hosted the institutions and personnel of government to a remarkable degree. The political events of the 1640s and 1650s led to the commandeering of aristocratic townhouses and other prominent buildings and public spaces in Westminster in a manner that held deep symbolic resonance. The chapter argues that the current notion of Westminster as ‘national space’, with its churches and buildings closely associated with state government, was very much a creation of the 1640s and 1650s.