Josef Zieleniec spent the greater part of his professional career working as an economist. Prior to the fall of the communist regime in Czechoslovakia in 1989, he worked first in the Institute of Research in Engineering Technology and Economics Research, and later at the Institute of Economics of the Czechoslovak Academy of Science. Apart from research in microeconomic theory, he dealt with problems of economic transition from a centrally planned to market economy. The study "Czechoslovakia at the crossroads", based on his research, had a significant impact on discussions of economic reforms after 1989. At the beginning of 1990 Josef Zieleniec together with Jan Švejnar founded The Center of Economic Research and Education (CERGE), the first American-style economics Ph.D. program in Central and Eastern Europe, at Charles University in Prague. He became its first director. He is the co-founder of the Civic Democratic Party (ODS) and acted as the Vice Chairman of the party since 1991. After the elections in 1992 Josef Zieleniec became Minister of International Relations of the Czech Republic (still part of the Federation), and was one was one of the negotiators of the separation of the Czechoslovak Federation. After the split of Czechoslovakia on 1 January 1993 Josef Zieleniec was appointed Minister of Foreign Affairs of the independent Czech Republic, and after the elections in 1996 also held the position of Deputy Prime Minister. As Minister of Foreign Affairs he opened and led negotiations that culminated in the Czech-German Declaration, the historical reconciliation between the two countries. In October 1997 Josef Zieleniec refused to accept a controversial decision on financing of the Civic Democratic Party and resigned from his governmental and party functions. After leaving the ODS he founded JZP, a consultancy dealing with investment banking and EU-related problems. In the spring of 2000 he was elected senator of the Czech republic. In the Senate he was a member of the Committee for Foreign Affairs, Defence and Security. During his term in the Senate he focused his efforts on European Integration-related topics. In 2002 he became a delegate of the Senate to the Convention on the Future of Europe. He worked in the Convention throughout its existence until July 2003 and is co-author of the draft EU Constitution. In the June 2004 European elections Josef Zieleniec was elected member of the the European parliament. He worked in the Committee of Foreign Affairs and the Committee of Economic and Monetary Affairs. Currently Josef Zieleniec is active mainly in the academic field, teaching international politics and other related topics.