Overview of Concordats in Germany
In this excerpt Prof. Francis Messner looks at Germany, where relations between church and state are regulated by treaties. This means international “concordats” for the Catholic Church, and national “accords” for the other religious groups. In the last hundred years there have been three waves of these.
The privileged position of the German churches reaches back to the 17th century when the Holy Roman Empire of the German Nation still had a patchwork of principalities where church and state were one.
However, the German churches' present favoured position in the constitution results from the 20th-century “Weimar church compromise”. The interwar Weimar democracy sought a constitutional middle way between a state church (as in Britain) and a private one (as in France). The two main German churches were not to be part of the state on the one hand, nor completely separate, on the other. Instead, they received intermediate status as "public corporations".
Treaties can be made with German churches because they are public corporations, not private ones. Being a public corporation allows the Church, as Cardinal Lehman puts it, to “be outside the private sphere” without being integrated into government. [*] Put less tactfully, this status means public money without public accountability.
Overview of German church-state treaties
Excerpt from Prof. Francis Messner's “État et religions en Europe”, 2004.
The practice of dealing with religious groups by means of treaties, (Vertragskirchenrecht) began after World War I when the abdication of the last Kaiser ushered in the Weimar Republic. The new Weimar Constitution separated church and state on the one hand , and made the churches self-governing on the other.  In order to bridge this gap between a religiously neutral state and religious groups which ran their own affairs [and many of Germany’s social services, as well], the government resorted to treaties. The power of the German churches was such that the state was obliged to negotiate with the churches over the laws that would govern them.
The Weimar articles on religion were taken over by the present German Constitution (1949). It is true that this national constitution, unlike the constitutions of several of the twenty states in the German federation, makes no explicit mention of treaties as a potential source of laws concerning religion. However, by assuming Weimar treaty obligations, it acknowledges the continuing validity of accords made with religious groups before 1919.  It also effectively permits the conclusion of new ones. This it does by giving to the individual German states jurisdiction over religion (by default ) and then allowing them to use this jurisdiction to conclude treaties with foreign countries, so long as they get permission from the national government.  [Actually, the Constitutional Court has ruled that in the case of concordats the individual states need no clearance from the national government.] 
The treaty law which governs religious matters in Germany necessarily leads to different kinds of accords. When treaty law is applied to concordats or to other conventions concluded with the Holy See, these are raised to the level of international law. By contrast, the accords with the traditional German Protestant churches, with Catholic dioceses or with other religious communities (Jews, Old Catholics, Orthodox, Methodists and even an occasional group of freethinkers) are merely accords under national public law.
In the century or so since church-state relations in Germany came to be governed by treaties, there have been three distinct flurries of concordat activity.
♦ The first was in the wake of the Weimar Constitution, when the goal of religious parity led to the individual German states signing both Concordats with the Holy See and accords with the territorial Protestant churches, either simultaneously or within several months of each other. This was the case in Bavaria (1924), Baden (1932) and Prussia (1929-31). Finally, in 1933, came Hitler’s concordat which is still in force and which regulated church-state relations at the federal level. Its Protestant counterpart never came about, perhaps, as Prof. Messner suggests, “because of the increasing conflict between the Nazi regime and the Protestant church in Germany” [or perhaps because the valuable international recognition provided by a concordat with the Vatican could not be offered by a purely national church]. After World War II, questions about the future of Hitler’s concordat led to a lull in church-state treaties.
♦ However, when the German Constitutional Court (Bundesverfassungsgericht) ruled in 1957 that Hitler’s concordat would remain in force, this set off a second wave of church-state treaties, resulting in over a dozen  treaties between various state governments and various religious groups. On the Catholic side this led to a concordat with Lower Saxony (1965), North Rhine-Westphalia (1984) and Saarland (1985). However, in predominantly Protestant Hesse the government refused to enter into a concordat. Therefore, the Vatican arranged for the treaties to be made with regional Catholic bodies: with the dioceses of Fulda, Limburg, Mainz and with the Archbishopric of Paderborn (1963). Known as the “Bishopric Treaties” (Bistumsvertraege) these resemble concordats and the preamble states that they are made “with the agreement of the Holy See”. 
Notes [added to Prof. Messner's text by the editor of Concordat Watch]
* "Lehmann warnt Staat vor Gleichgültigkeit gegenüber Christentum", DDP, 19 June 2007.
1. Cf. the Weimar Constitution http://www.zum.de/psm/weimar/weimar_vve.php (WRV), 1919. The parts of it relating to religion which were taken over by the present German Constitution, 1949 are listed at the end under “Appendix to Basic Law” http://www.psr.keele.ac.uk/docs/german.htm For separation of church and state see, for example, WRV Art. 136.1: “Civil and political rights and duties are neither dependent upon nor restricted by the practice of religious freedom”; WRV Art. 137.1: “There is no state church.”
2. Ibid., WRV Art. 137.3: “Each religious body regulates and administers its affairs independently within the limits of general laws….”
3. WRV Art. 138.1: “State contributions to religious communities, inasmuch they are based on law, treaty or specific legal claim, are to be handled by state legislation.” [This seems to be missing from the (smoother) translation of the Weimar Constitution available in the Constitution or Grundgesetz, (GG.]
4. Basic Law for the Federal Republic of Germany (Grundgesetz): GG Art. 70.1: “The Laender [individual German states] have the power to legislate insofar as this Basic Law does not confer legislative powers on the Federation”.
5. GG Art 32.3: “Insofar as the Laender have power to legislate, they may, with the consent of the Federal Government, conclude treaties with foreign states”.
6. [Constitutional Court Judgement of 26 March 1957, III. 2. (BVerfG, Urteil vom 26. März 1957 - 2 BvG 1/55 - KirchE Bd. 4, S. 91.)
7. "Staatskirchenvertrag", Wikipedia. Listed (in German) under "Kirchenverträge".
8. [Bishopric Treaty] between the State of Hesse, on the one hand, and the dioceses of Fulda, Limburg, Mainz and Archbishopric of Paderborn, on the other, 9 March 1963.