RésuméToday's tendency to privatize or outsource many activities hitherto considered the exclusive preserve of the State has given rise to sharp debate. This phenomenon is of direct concern to humanitarian organizations when it involves essential public services such as the water supply and health care. Privatizing the realms of defence and security — the very core of State prerogative — raises serious legal and humanitarian questions. In this article the author takes a brief look at developments in the interaction between the State and the private sector, as well as at the emergence of the non-profit sector. The specific nature of humanitarian emergencies brings out in particularly stark contrast some of the main challenges related to the privatization and outsourcing of public services and security. The author dwells in particular on the privatization of military functions (including the running of detention places), of health care and of the supply of drinking water. He examines the role, responsibility and obligations of the various parties concerned. The economic rationale behind these practices is put into question, as well as the compatibility between the corporate motive of profit-maximization, on the one hand, and the need to ensure public security and health on the other. The author suggests that humanitarian agencies need to better understand how the private sector operates and how they may interact with it. There is a need to better assess both the potential benefits and risks resulting from the current privatization and outsourcing trend — with the ultimate objective of ensuring more effective protection and assistance for people affected by war.