Bernhard Zaglmayer Researcher, Institute of Social Law K.U. Leuven (Catholic University of Leuven) Paul Schoukens Professor of Social Security Law K.U. Leuven, and General Coordinator, European Institute of Social Security Danny Pieters Professor of Social Security Law K.U. Leuven, and Secretary-General, European Institute of Social Security Cooperation Between Social Security and Tax Agencies in Europe Collaboration Series APRIL 2005