At first the organisation represented a loose association of churches, but with the adoption of a Constitution at the 1964 Assembly a significant step was taken towards forming a regional conference of churches. This Assembly was held at sea, aboard the m.v. Bornholm, in order to overcome last-minute visa difficulties.

The fifth Assembly in 1967, held in Pörtschach, Austria, created a full time secretariat as from April 1968. Subsequent Assemblies were held in Nyborg Strand (1971), Engelberg, Switzerland (1974), Chania, Crete (1979), Stirling, Scotland (1986), Prague, former CSFR (1992) when a radically revised Constitution was adopted, Graz, Austria (1997) and Trondheim, Norway (2003).

A new Constitution (PDF) was adopted in Budapest (2013), the document is also available in French (PDF) and German (PDF). Upon the finalisation of the merger between the Church and Society Commission and the Conference of European Churches in 2014, a final legal text based on the Constitution was prepared in French according to Belgian law. This is the only legally-binding constitution.