The medieval duchy of Brabant was one of the most powerful principalities of the Low Countries. During the second half of the fourteenth century, it underwent a particularly dramatic period in its history: the House of Leuven was on the point of disappearance, the duchy was coveted by Philip the Bold of Burgundy, who was already dreaming of extending the 'Burgundian Empire' and, by a network of alliances, Brabant was drawn into the Hundred Years' War. The author reviews the successive conflicts which troubled the duchy between 1356 and 1406; the different authorities which influenced the course of military operations (the duchess and the duke, their officers, and the Estates of Brabant); describes the combatants, in particular the nobility and the urban militias; considers the practical aspects of warfare; and analyses the military obligations and contracts which bound the men at arms to the duke. SERGIO BOFFA is currently researching in the department of Maps and Plans, Bibliotheque Royale de Belgique, Brussels.