What is orthodoxy? In recent controversies in the Church of England and in the wider Anglican Communion, those who insist that the Church's traditional teachings about marriage and celibacy cannot be altered are increasingly described as 'orthodox', a claim that has been disputed on the ground that orthodoxy is defined by the great creeds and confessions of the Church, none of which mentions the subject. This Briefing argues that orthodoxy extends well beyond what the creeds and confessions state. It is rooted in the mind of Christ, which is revealed to us in Holy Scripture and encompasses every aspect of life, including our doctrine and practice of matrimony. Orthodoxy is expressed not only in creeds but also in the forms of our worship, not least in the rich tradition of hymnody that has stood the test of time. Christians of every tradition resonate with orthodoxy because it bears witness to the presence of the Holy Spirit in our hearts, as he illuminates and applies the Word of God to our lives. Using the words of the well-known hymn The Church's One Foundation, Gerald Bray demonstrates what orthodoxy is and why it matters both to individual believers and to the Church as a whole. In every generation we are challenged by new heresies and divisions that seek to lead us astray. Orthodoxy is the unchanging teaching of Christ given to us in the Bible as the resource we need to combat them. It unites us with the saints of the past, the present and the future in the spiritual warfare that engages God's people as we make our way to the heavenly kingdom promised to all true followers of Jesus.