The campaigns in Iraq and Afghanistan have had profound effects on both the British and US militaries. Among the most important is the way in which they have challenged traditional assumptions about the character of unconventional conflict and the role of the military within comprehensive strategies for encouraging sustainable peace. In the UK, the most important doctrinal response has been JDP 3–40 Security and Stabilisation: the military contribution. Security and Stabilisation is an ambitious attempt to synthesize elements of counterinsurgency, counterterrorism, peace support and state-building within a single doctrine that reflects the lessons learned from recent British operational experience. This article examines the purpose, impact and potential value of this important innovation in British doctrine. To do so, the article explores the genesis of Stabilization; analyses its impact upon extant British doctrine for counterinsurgency and peace support; discusses its relationship with the most important related US doctrines, FM 3–24: the counterinsurgency field manual and FM 3–07: the stability operations field manual; and debates the function of doctrine more broadly. It concludes by summarizing the primary challenges Security and Stabilisation must overcome if it is to make a serious contribution to the theory and practice of such complex interventions.