Jón Viðar Sigurðsson is a Professor of History in the Institutt for arkeologi, konservering og historie, University of Oslo. He is the author of a large number of monographs and articles on Medieval Scandinavia including Den vennlige vikingen. Vennskapets makt i Norge og på Island ca. 900-1300 (Oslo, Pax, 2010), and Chieftains and Power in the Icelandic Commonwealth (Transl. Jean Lundskær-Nielsen, Odense 1999).Timothy Bolton is an independent scholar and an honorary fellow of the School of History, University of Wales, Cardiff. He is the author of a monograph on The Empire of Cnut the Great: Conquest and the Consolidation of Power in Northern Europe in the Early Eleventh Century (Leiden and Boston: Brill, 2009), as well as a number of articles on Anglo-Saxon and Medieval Scandinavian history.