Peggy K. Liss, "Isabel the Queen," New York: Oxford University Press, 1992, p. 165
James Reston, Jr. "Dogs of God," New York: Doubleday, p. 18.
Douglas Biggs, “A Wrong Whom Conscience and Kindred Bid Me to Right: A Reassessment of Edmund of Langley, Duke of York and the Usurpation of Henry IV” Albion, 26 (1994), pp. 231–246.
Douglas Biggs, “To Aid the Custodian and Council: Edmund of Langley and the Defense of the Realm, June–July 1399,” Journal of Medieval Military History, I (2002), pp. 125–144.
Douglas Biggs, “’A Voyage or Rather and Expedition to Portugal:’ Edmund of Langley in Iberia 1381/82,” Journal of Medieval Military History 7 (2009), pp. 57–74.
Douglas Biggs, Three Armies in Britain: The Irish Campaign of Richard II and the Usurpation of Henry IV, 1399, Brill Academic Publishers, Leiden, The Netherlands, 2006.