Stein D. Tønnesson is a Norwegian historian. He was the director of the Peace Research Institute Oslo (PRIO) 2001-09, 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. Tønnesson has also worked as a journalist. His interests the past decade has been in particular global history, globalization and the decades of relative peace in south east Asia since 1979.