The article is devoted to the issues of international regional tax integration. The international economic integration has two mainstreams: global and regional economic integration. The global tax integration is concerned only with double taxation matters while the regional tax integration aims at procuring of four fundamental freedoms of common market and goes far beyond the elimination of double taxation. The legal solution for both global and regional international tax integration can not be found on the base of traditional conflict of laws method (sometimes called collision technique). Only the substantive law instruments meet the needs of both types of tax integration. The experience of international regional tax integration shows the examples of integration (or community) tax law system formation which include both supra-national and national sources of law. The tax harmonization is usually started with indirect taxes and indirect taxes harmonization reaches the highest level. The tax harmonization covers the tax administration issues. The direct taxes are usually harmonized later and only with reference to selected issues. Taxes are part of sovereignty which is vested in particular state therefore supra-national entities do not have their own tax systems.