The Oxford Handbook on Women, Peace, and Security examines the significant and evolving international Women, Peace, and Security (WPS) agenda, which scholars and practitioners have together contributed to advancing over almost two decades. Fifteen years since the passage of United Nations Security Council Resolution 1325 (2000), the WPS agenda has never been more salient on the agenda of states and international organizations. The Global Study of 1325 (“Preventing Conflict, Securing Peace”) commissioned by the UN Secretary-General and released in September 2015, however, found that there is a major implementation gap with respect to UNSCR 1325 that accounts for the gaping absence of women’s participation in peace and transitional decision-making processes. With independent, critical, and timely analysis by scholars, advocates, and policymakers across global regions, the Oxford Handbook synthesizes new and enduring knowledge, collectively taking stock of what has been achieved and what remains incomplete and unfinished about the WPS agenda. The handbook charts the collective way forward to increase the impact of WPS research, theory, and practice.