Juridical ecumenism is a branch of ecclesionomology: the study of church law as a form of applied ecclesiology. It involves the comparative study of the laws and other regulatory entities of different ecclesial traditions and their institutional churches, as well as the practice of church law and ecumenism. It does not seek to replace the historic focus on theology and doctrine in ecumenical dialogue, but rather to remedy the missing legal link in the ecumenical enterprise to date, by using church laws as a rich unifying instrument for greater visible communion between separated institutional churches. One fruit of juridical ecumenism is the issue of the Statement of Principles of Christian Law by an Ecumenical Panel in 2016 and its launch at the 11th Assembly of the World Council of Churches in 2022. Marking the 1700th anniversary of the great Council of Nicaea and its Canons gives us the opportunity to think critically, as an exercise in juridical ecumenism, about continuity and change over the centuries in the nature of church law. We can achieve this by comparing the Statement of Principles of Chistian Law (2016) issued by the Ecumenical Christian Law Panel with the Nicene Canons (325) issued by the first Ecumenical Council. This article explores the similarities and differences between these two juridical entities – in terms of their (1) nature, authority, and reception; (2) subject matter; (3) sources; (4) purposes; and (5) internal structure – and what the Nicene Canons and the Christian Law Principles tell us about these five aspects of church law itself. I conclude with reflections on the value of comparison for the future of juridical ecumenism.