This chapter highlights the historical evolution of the issue of rapid reaction and of predictable capacities, and outlines some of the major institutional, operational, financial, and political challenges that need to be taken into consideration on the path towards establishing such tools. It reviews Standby High Readiness Brigade for UN Operations origins, policies, and the key lessons that can be learned in terms of major obstacles and difficulties related to the creation and maintenance of a United Nations (UN) multinational rapid reaction force. The chapter examines the inter-organizational dimension related to the UN’s cooperation and rivalry with the European Union, North Atlantic Treaty Organization, and the African Union in the realm of rapid reaction. It highlights some of the most pressing problems and obstacles encountered when designing and implementing rapid reaction mechanisms for the United Nations. Rapid reaction depends on a tricky mix of organizational capacity and national political will.