B. 1937. Studied at the Faculty of History of the University of Warsaw. 1959–1961: scholarship from Fondazione Giorgio Cini in Venice. Began his research at the Institute of History, University of Warsaw, from which he was dismissed for political reasons. Worked at the Institute of History of Material Culture, Polish Academy of Sciences. During the communist period in Poland – democratic opposition activist and co-founder of the Solidarity movement. Arrested and imprisoned several times for, among others, an open letter to the communist party and for trade union-related activities. Between 1989 and 1991 Senator of the Republic of Poland. Professor since 1990. 1992–1994: lecturer at the University of Wrocław. Since 1994 has worked at the Institute of History, University of Warsaw. Has also lectured at École des Hautes Études en Sciences Sociales and Collège de France in Paris, and the La Sapienza University of Rome. Author of numerous academic publications on medieval history which have won a number of prestigious awards.
- Zajeździmy kobyłę historii. Wyznania poobijanego jeźdźca, Warszawa 2013;
- Scènes de grèves en Pologne, Lozanna 2006;
- Barbarzyńska Europa, Warszawa 2004;
- Życiodajny impuls chuligaństwa. Notatki z lat 1993–2002, Kraków 2003;
- Opole, centena, pagus. Versuch einer komparativen Auffassung der Langemeinde und Territorialverwaltung, [in:] Das Reich und Polen, Konstancja 2003, pp. 423–438;
- Czy opole istniało, Przegląd Historyczny, vol. 92, 2, 2001, pp. 161–185;
- Zemsta, okup i podmiot moralny w prawach barbarzyńskich, [in:] Aetas media, aetas moderna. Studia ofiarowane profesorowi Henrykowi Samsonowiczowi w siedemdziesiątą rocznicę urodzin, Warszawa 2000, pp. 273–285;
- Dokąd od komunizmu?, Warszawa 1993;
- Chłopi w społeczeństwie polskim, Wrocław 1987;
- Organizacja gospodarcza państwa piastowskiego X-XIII wiek, Wrocław 1975, Poznań 2000;
- Revolutionary marxist students in Poland speak out (1964–1968), Nowy Jork 1969;
- List otwarty do partii (with Jacek Kuroń), Paryż 1966.