Professor Decker's teaching and research interests include sustainability and corporate responsibility, global corporate strategies, governance systems, business organisations, comparative political economy, Western Europe and the European Union.

He was the Vice Chair (1991–1993) and President and CEO (1971–1990) of the Siemens Corporation USA, based in New York.  Prior to that, he served at Siemens Corporation’s Central Finance Division, Munich (1970) and at the Legal Department (1958–1969).

Professor Decker received his law degree from the University of Heidelberg (1953), passed the German Bar Exam (1957), and holds a Doctorate of Law (1958).  He is the President of the Heidelberg University Association.
 
He currently serves on the Board of Governors of the New School University (New York) and on the board of International House (New York) and the European Institute (Washington, D.C.).  He is also a board member at the Education Development Center (Boston).