Dennis is Professor of Macroeconomics and Sustainability at the Hertie School in Berlin, the President of the Global Solutions Initiative, Senior Research Fellow at the Blavatnik School of Government in Oxford University, and a Non-Resident Senior Fellow at the Brookings Institution in Washington, D.C. He is an expert on labor economics and public policy and is well-known for the insider-outsider theory of employment and unemployment which he developed together with Assar Lindbeck. Dennis has acted as an adviser to a variety of international organizations and national governments and has published extensively on employment policy, the design of social systems, caring economics, and monetary and fiscal policy.