Complex UN peace operations represent an ambitious tool to stabilize war-torn territories. They often fail to live up to expectations, but there are exceptions. The study explores an alternative explanation for the performance of such missions, applying an organizational theoretical perspective. The argument of the book is threefold. From the outset, UN missions operate under unfavorable conditions: they are constrained by political considerations of member states, by rigid rules and scarce resources, and they face adverse on-the-ground conditions. Under these circumstances, so-called organizational pathologies develop. The more virulent these malpractices turn, the more likely failure may become. The success of peace operations thus depends to a great part upon the ability to cope with pathologies. The study identifies these coping strategies, systemizes them, and elaborates on the crucial role of the mission leadership. By means of two detailed case studies on the UN missions in Eastern Slavonia/Croatia and East Timor, including numerous interviews with UN experts and practitioners, the study gives a theoretically informed insight into the transitional management of UN operations.