This chapter examines the use of martial law powers during four frontier wars against the Xhosa people, in 1835, 1846, 1850 and 1877, and two rebellions by mixed-race ‘Hottentot’ and Griqua people, and discusses the debates over the nature of martial law which followed. During the first two wars, martial law powers were largely used to facilitate the raising of troops, but questions were raised about whether martial law could be used to govern newly acquired areas. As the debates over the status of the territory east of the Keiskamma river showed, martial law could not be used to govern land incorporated into the colony, but it could be used to administer conquered lands. Martial law powers were also used to conduct trials and imprison rebels in 1851 and 1878, which led to debates between law officers in London and Cape Town regarding the nature of these powers. In these debates, the law officers endorsed the English common lawyers’ view which had emerged after 1865. A strong commitment to the rule of law was also expressed by the Cape Supreme Court when dealing with the case of Griqua prisoners, detained without trial at Cape Town after the rebellion of 1878.