This article looks briefly at three main types of cross-border operations in humanitarian history, and then addresses two main questions: can cross-border operations be pursued legally?; and what constitutes ethical crossborder operations? The legality of cross-border humanitarian operations turns mainly on the two issues of the consent of the affected state and the exclusively humanitarian character of any crossborder aid. Under international humanitarian law (IHL), the consent of the state in whose territory operations are to be implemented is required. So too is the consent of the neighbouring state from which any cross-border operation is to be mounted. In practice, consent is also required from any non-state armed actor in effective control of territory through which the relief goods must transit or for whose civilians they are intended. If the law allows cross-border humanitarian operations in certain situations, what are the main ethical considerations in the decision to pursue such operations? Like most humanitarian decision-making, these turn on issues of need, context and capability, and issues of principle around impartiality, neutrality and independence.