'Orthodoxy' and 'heresy' are essential categories by which the 'Catholic' theological tradition evaluates the (im)propriety of various beliefs and practices relative to its non-negotiable commitments. This Element sketches moments in the development of Christian 'orthodoxy' and 'heresy' in time, as much in the Old and New Testament as in the history of the Church. It also touches upon the vexed theological-methodological question of the relation between Scripture and ecclesial Tradition before concluding with a critique of the 'Catholic' tradition's preoccupation with 'orthodoxy' and 'heresy' in favor of a Christian theology 'without anathemas' that is concerned only for truth.