Stein Dorenfeldt Tønnesson (born 2 December 1953), is a Norwegian historian.
He was the director of the Peace Research Institute Oslo (PRIO) from 2001 to 2009, when he was replaced by Kristian Berg Harpviken.
Stein Tønnesson stays on at PRIO as a Research Professor, while at the United States Institute of Peace (USIP) as Jennings Randolph Senior Fellow 2010-11.
Tønnesson's foremost research efforts have been revolution and war in Vietnam, national identity in South-East Asia, the South China Sea conflict, and Norwegian sports history.
Stein Tønnesson has worked as Professor of Human Development Studies at the Centre for Development and the Environment (SUM) at the University of Oslo, and has also been a senior research fellow at the Nordic Institute for Asia Studies (NIAS) in Copenhagen.