<P>Since the end of the Cold War attacks on aid workers have surged as they have come to be viewed by some militants as a prized political targets and by criminals as lucrative resources to extort from or ransom. In response humanitarian agencies have struggled to determine with what measures are morally and politically appropriate to ensure the physical safety of their personnel. </P><P></P><P>Despite the growth and significance of the interaction between humanitarian agencies and private security contractors there has been little analysis of the phenomenon and its accompanying tradeoffs. This work seeks to examine why the principles and practices of humanitarian agencies changed from the conventional practice of refusing to engage private security contractors for protection and how such security arrangements have become palatable to humanitarian agencies.</P><P></P><P>Providing a much needed addition to the field, this work:</P><P></P><UL><P><LI>Examines the core influences on humanitarian action; notably, the push and pull factors associated with politics, force, and markets. By framing the dilemmas inherent in security problems, a clearer examination of security solutions is offered. </LI><P></P></UL><P></P><UL><P><LI>Traces particularities of key humanitarian agencies in realizing or resisting this innovation in security arrangements. The documentation and juxtaposition of diversity of values and experiences of different humanitarian agencies calls attention to and explains variation within the sector.</LI><P></P></UL><P></P><UL><P><LI>Evaluates the consequences of humanitarian agencies hiring security contractors. A review of cases where private security has been contracted to protect aid workers illuminates for both agencies that engage in the practice and those that do not, but also speaks to trends in the nature of humanitarian action.</LI><P></P></UL><P></P><P>This work will be valuable reading for students, policy makers and aid workers alike. </P>