Reuven S. Avi-Yonah (Michigan) has posted Double Tax Treaties: An Introduction on SSRN. Here is the abstract:

The existing network of over 2,500 bilateral double tax treaties (DTTs) represents an important part of international law. The current DTTs are all based on two models, the OECD and UN model DTTs, which in turn are based on models developed by the League of Nations between 1927 and 1946. Despite some differences that will be discussed below, all DTTs are remarkably similar in the topics covered (even the order of articles is always the same) and in their language. About 75% of the actual words of any given DTT are identical with the words of any other DTT. Thus, the DTT network is the most important element of the international tax regime, i.e., the generally applicable rules governing income taxation of cross-border transactions. Indeed, I have argued that given the similarities among all DTTs, certain rules embodied in them (such as the requirement to prevent double taxation by granting an exemption or a foreign tax credit) have become part of customary international law, and therefore may be binding even in the absence of a DTT.