In this chapter I enquire, what role does constitutionalisation play in secularisation? In particular, I will ask whether the constitutionalisation of a European legal order plays a role in secularisation. By ‘constitutionalisation’ I do not mean necessarily the adoption of a document entitled ‘constitution’, but rather a fundamental legal ordering, underpinning the state or a supra-state entity. All European states are based on a constitutional order, including the UK, which does not have a written constitution. The secular or religious nature of each European state is formulated by its constitution, but also by European regional treaties, which have constitutional implications for their member states.

The status of religion within constitutions is interesting and unique, because of the primordial character of religion as a social and political institution. In the emergence of modernity, constitutionality of states has superseded religion (or divine authority) as the fundamental legitimate source of authority. But this is by no means a completed or irreversible process. Even within the modern nation state, including in European states, remnants of an earlier order remain. Any national or international legal regulation necessarily operates over these underlying historical layers.

I will look at one important example of constitutional change: the role played by the European Convention on Human Rights, a fundamental legal document of the Council of Europe, in changing the legal landscape of Europe, and ask whether it led to secularisation in European states.