Alongside the familiar pitched battles, regular sieges, and large-scale manoeuvres, medieval and early modern wars also involved assassination, abduction, treason and sabotage. These undercover operations were aimed chiefly against key individuals, mostly royalty or the leaders of the opposing army, and against key fortified places. However, because of their clandestine nature, these deeds of "derring-do" have not been studied in any detail, a major gap which this book fills.