The Heidelberg Catechism is a Protestant confessional document taking the form of a series of questions and answers, for use in teaching Reformed Christian doctrine. It has been translated into many languages and is regarded as one of the most influential of the Reformed catechisms. The Catechism is divided into fifty-two sections, called "Lord's Days," which were designed to be taught on each of the 52 Sundays of the year. The Synod of Heidelberg approved the catechism in 1563. In the Netherlands, the Catechism was approved by the Synods of Wesel (1568), Emden (1571), Dort (1578), the Hague (1586), as well as the great Synod of Dort of 1618-1619, which adopted it as one of the Three Forms of Unity, together with the Belgic Confession and the Canons of Dort. (courtesy of wikipedia.com)