Claudia E. Haupt, Transnational Nonestablishment, 80 George Wash. L. Rev. 991 (2012)
This article is set in the context of the widespread entrenchment in international law of the right to freedom of religion without the concomitant (to many American eyes) entrenchment of a principle of nonestablishment. Haupt intriguingly argues that a recent trend towards nonestablishment might be gleaned from a review of European Court of Human Rights cases dealing with religious freedom. Haupt says:
"Under the [European Convention on Human Rights], we may be observing an emerging trend toward nonestablishment. A number of recent [European Court of Human Rights] decisions addressing the relationship between religion and the state in democratic societies seem to implicitly assume a nonestablishment principle. This trend is normatively supported by developments on the EU level and in individual European countries." (p. 1004)
Haupt argues that the "textual anchor" for this trend towards nonestablishment is actually contained in a clause in the Convention that serves as a limitation on the right to freedom of religion: Article 9(2). She goes on to discuss several cases that she argues demonstrates the existence of this trend (pages 1008-1012), but also discusses an arguable counter-example, Lautsi. She also concedes that many individual European countries have various forms of establishment domestically.
I'm not familiar enough with the Convention or the decisions that Haupt cites to evaluate how persuasive the claim of an emerging trend is. I can say that the article is thorough, well-researched, and balanced. The treatment of the nonestablishment principle in international law is an important topic, and well-worth watching closely.