This practice note focuses on planning and implementing SSR activities in stabilization environments. Stabilization environments are characterized by circumstances related to descent into, continuation of, or emergence from conflict in which the physical security, economic, political, and humanitarian needs of the population are often far greater than the resources available to meet them. In addition to the challenges of SSR in any context (e.g., shifting power dynamics, limited resources, reconciling donor and host state priorities), SSR in stabilization environments faces challenges exacerbated by the context: security (ongoing threats to civilians and the state), governance (weak state capacity, fragmented authority, destroyed infrastructure), and social fragmentation (divisions within and among communities). As the degree of “permissiveness” increases, in a gradual and uneven process, long-term security sector reform programming may be developed in consultation with host state stakeholders and implemented. Given the variation in possible stabilization environments, this practice note on SSR and stabilization focuses on decision-enabling and planning tools for SSR assistance providers (e.g., maintaining flexibility, adjusting expectations, options for engaging with non-state actors, and setting the preconditions for long-term SSR) and on building the capacity of local actors to support decision-making and ownership. SSR must be able to seize windows of opportunity, respond quickly, and adjust appropriately to the context, to changing power dynamics, and to unintended consequences of SSR initiatives.