In a globalized tax world, the national means of the tax authorities are limited and are not sufficient to realize the tax claims. An increasing number of legal sources exist to overcome the gap between the worldwide taxation and the limited territorial power of the national tax authorities: e.g. the EU Council Directives concerning mutual assistance in the field of direct taxation and for the recovery of claims, the EU Council Regulation on administrative cooperation in the field of VAT, Articles 26 and 27 OECD Model Convention as patterns for bilateral agreements of information exchange and mutual assistance in tax collection, the OECD Model 2002 for a specific bilateral Tax Information Exchange Agreement (TIEA) which has recently been used for agreements with tax haven countries, the Convention of the Council of Europe/OECD on mutual administrative assistance in tax matters of January 25, 1988, and unilateral legal sources. The OECD and EU are forcing the Automatic Exchange of Information (AEOI) Approach to deal with financial accounts, similar to what the US is implementing, in a network of Foreign Account Tax Compliance (FATCA) Agreements. The course aims to provide a systematic understanding of the content, scope, and relationship of these legal sources. Furthermore, the course will show the tension between the need for an efficient exchange of information, on the one hand, and the need of legal protection of the taxpayer against violation of his commercial or professional secrets, on the other.