The Second Vatican Council (1962–5), or Vatican II, is arguably the most significant event in the life of the Catholic Church since the age of the Reformation in the 1500s. The Council initiated, intentionally or not, profound changes not simply within Catholic theology, but in the religious, social, and moral lives of the world’s c.1 billion Catholics. It also reconfigured, intellectually and practically, the Church’s engagements with those outside it—most obviously with regard to the Jews and members of other Christian denominations. The 16 documents formally issued by Vatican II constitute some of the most influential, concretely impactful, and most-cited theological writings of the whole 20th century. Debates over their correct interpretation and authority are constant, but they remain an indispensable point of reference for all areas of Catholic life, from liturgy and sacraments to the Church’s vast network of charitable and educational endeavours the world over. In this Very Short Introduction, Shaun Blanchard and Stephen Bullivant present the backstory, event, and reception with freshness and dynamism. Vatican II is explored in light of the wider history of the Catholic Church and placed in the exciting and tumultuous context of the 1960s. The perfect introduction for academics and for undergrad or postgrad classrooms, this Very Short Introduction distils the best research on Vatican II, employing cartoons, the first-hand accounts of participants and observers, and the official proceedings of the Council to paint an exciting and rich picture of one of the most important events of the last century.