Drafted by the Westminster Assembly of Divines meeting at Westminster Abbey in London from 1643 to 1649 during the English Civil War. 121 divines (plus Scottish commissioners) worked for five and a half years to produce: the Westminster Confession of Faith (33 chapters), the Larger Catechism (196 Q&A), the Shorter Catechism (107 Q&A), a Directory for Public Worship, and a Form of Church Government. The project's purpose was to standardize doctrine, worship, and polity across the three kingdoms (England, Scotland, Ireland). It became the doctrinal standard of Presbyterian churches worldwide — adopted by the Church of Scotland in 1647 and used ever since.
The Westminster Confession is the high-water mark of systematic Reformed theology. It opens with a magnificent chapter on Scripture ("The authority of the Holy Scripture... dependeth not upon the testimony of any man or church, but wholly upon God"), continues through the classical Reformed doctrines (God and the Holy Trinity, God's eternal decree, creation, providence, the fall, the covenants, Christ the Mediator, free will, effectual calling, justification, adoption, sanctification, saving faith, repentance, good works, perseverance, assurance, the law, Christian liberty, worship, oaths, the civil magistrate, marriage, the Church, the sacraments, baptism, the Lord's Supper, Church censures, synods, the last things). Virtually every Presbyterian, many Reformed, and most Reformed Baptist churches (via the 1689 London Confession which closely parallels Westminster) confess some version of this document. The Shorter Catechism opens with what is often called the most beautiful sentence in English theology: "Man's chief end is to glorify God, and to enjoy Him forever." That one line summarizes the whole Reformed vision of life.