Welsh constitutional development in recent times is characterized by a convoluted and ongoing set of legislative transformations and by the emergence of a distinct policy approach not only for the sub-state polity itself but also under the banner of a ‘new Union’ for the United Kingdom as a whole. Examination of the design and dynamics of the Wales Act 2017 serves to illuminate the difficulties and rewards of the territorial constitutional journey, especially in terms of central government conservatism in the face of principled argument and of the scope afforded for home-grown democratic renewal. In terms of the extended Brexit process, where competing conceptions of the UK territorial constitution are brought to the fore, the Welsh Labour Government is seen combatting potentials for centralization under the rubric of a ‘UK internal market’, deal-making in the name of mutual benefit, and championing a new brand of shared governance in the UK. Today, the workings of the justice system in Wales are being examined on their own for the first time in two centuries by an independent commission established by the Welsh Government. With a new stage in the Welsh constitutional journey in prospect, a series of foundational questions is raised. This chapter reviews the key elements of the arrangements made for devolving legislative and executive power to Scotland, Wales, and Northern Ireland, explaining how these arrangements have developed over time and are still doing so. Particular attention is paid to the implications of the result of the independence referendum in Scotland in September 2014, not just for Scotland but also for England. Consideration is given to how mechanisms for making devolution work more effectively might be devised and to what the effects might be on devolution if the UK’s membership of the EU or its commitment to the European Convention on Human Rights are seriously called into question.