This study explores the ethical challenges that the International Rescue Committee (IRC) faced in its work with detained migrant and asylum-seeking populations in Greece and Libya over the past four years. It is intended not only to examine the IRC’s engagement with humanitarian principles in those two locations, but to offer a foundation upon which the IRC can explore how principled humanitarian action may be pursued in the face of constraints in other operational contexts where the agency works with populations in detention or detention-like circumstances.