Born in 1952. MA 1976, University of Warsaw; PhD 1986, post-doctoral degree (habilitacja) 2000 (both at UW); titular professor since 2013. Between 1976 and 1977 intern at the UW, dismissed for political reasons (collaboration with the independent Committee for Social Self-Defence KOR). In 1977-1981 director of the “Głos” and “Krąg” underground publishing houses. Restored to his position at the IH UW in 1980; worked there as assistant lecturer (1980-1986) and assistant professor (1986-1993). On leave between 1993 and 2000. In 1993-2001 secretary general of the Polish National Commission for UNESCO. UW professor since 2002. Since 1994 editor-in-chief of the Quaestiones Medii Aevi Novae annual journal. In 2000-2002 chair of the Organising Committee of the First Congress of Polish Medievalists and in 2001-2012 chair of the Standing Committee of Polish Medievalists. Member of the International Advisory Committee of UNESCO’s "Memory of the World" programme (1997-2001), and (2001-2005) chair of the programme’s Register Sub-Committee. Between 2004 and 2005 chair of the Mayor’s Commission for assessing the damages suffered by Warsaw and its inhabitants during the occupation period of 1939-1945. In 2008-2012 professor at the University of Paris-Sorbonne.