
TheHeidelberg Catechism (1563), one of theThree Forms of Unity, is aReformedcatechism taking the form of a series of questions and answers, for use in teaching Reformed Christian doctrine. It was published in 1563 inHeidelberg,Germany.[1]: 230 Its original title translates toCatechism, or Christian Instruction, according to the Usages of the Churches and Schools of the Electoral Palatinate. Commissioned by theprince-elector of theElectoral Palatinate, it is sometimes referred to as the 'Palatinate Catechism.' It has been translated into many languages and is regarded as one of the most influential of the Reformed catechisms. Today, the Catechism is "probably the most frequently read Reformed confessional text worldwide".[2]: 13
Frederick III, sovereign of theElectoral Palatinate from 1559 to 1576, was the first German prince who professed Reformed doctrine although he was officially Lutheran. ThePeace of Augsburg of 1555 originally granted toleration only for Lutherans under Lutheran princes (due to the principle ofcuius regio, eius religio). Frederick wanted to even out the religious situation of his highly Lutheran realm within the primarily Roman CatholicHoly Roman Empire. He commissioned the composition of a new catechism for his realm, which would serve to both teach the young and settle the differences in doctrine between Lutherans and the Reformed.[1]: 230–231 One of the aims of the catechism was to counteract the teachings of theRoman Catholic Church as well as those ofAnabaptists and 'strict'Gnesio-Lutherans likeTilemann Heshusius (recently elevated to general superintendent of the university)[3] andMatthias Flacius, who were resisting Frederick's Reformed influences, particularly on the matter of theEucharist.
The Catechism based each of its statements on Biblical source texts (although some may call them 'proof-texts' which can have a negative connotation), but the 'strict' Lutherans continued to attack it, the assault being still led by Heshusius and Flacius. Frederick himself defended it at the 1566Diet of Augsburg as based in Scripture rather than based inReformed theology when he was called to answer to charges, brought byMaximilian II, of violating thePeace of Augsburg. Afterwards, the Catechism quickly became widely accepted.[3]
A synod in Heidelberg approved the catechism in 1563. In theNetherlands, the Catechism was approved by the Synods of Wesel (1568), Emden (1571), Dort (1578), the Hague (1586), as well as the greatSynod of Dort of 1618–19, which adopted it as one of theThree Forms of Unity, together with theBelgic Confession and theCanons of Dort.[4] Elders and deacons were required to subscribe and adhere to it, and ministers were required to preach on a section of the Catechism each Sunday so as to increase the often poor theological knowledge of the church members.[4] In many Reformed denominations originating from the Netherlands, this practice is still continued.

While the catechism's introduction credits the "entire theological faculty here" (at theUniversity of Heidelberg) and "all the superintendents and prominent servants of the church"[5] for the composition of the Catechism,Zacharius Ursinus (1534–1583) is commonly regarded as the catechism's principal author.Caspar Olevianus (1536–1587) was formerly asserted as a co-author of the document, though this theory has been largely discarded by modern scholarship.[6][7]Johann Sylvan,Adam Neuser, Johannes Willing,Thomas Erastus, Michael Diller, Johannes Brunner, Tilemann Mumius, Petrus Macheropoeus, Johannes Eisenmenger,Immanuel Tremellius andPierre Boquin are all likely to have contributed to the Catechism in some way.[8] Frederick III himself wrote the preface to the Catechism[9] and closely oversaw its composition and publication.[1]: 230–231
Ursinus was familiar with the catechisms ofMartin Luther,John Calvin,Jan Łaski andLeo Jud and was therefore likely influenced by them, however the Catechism does not betray a patchwork nature but a unity of style.[1]: 233 There are three major scholarly traditions identifying the primary theological origin or influences of the Catechism: the first as 'thoroughly Calvinistic' or associated with theGenevan Reformation, the second as Reformed in the spirit of theZurich Reformation andHeinrich Bullinger and the third as equally Reformed and Lutheran (especiallyMelanchthonian).[2]: 14 The third tradition is justified by the fact that Frederick III himself was not thoroughly Reformed, but in his life represented a shift from a "Philippist/Gnesio-Lutheran theological axis to a Philippist-Reformed theological axis", which was especially evident in his attraction to the Reformed position on the Eucharist during a formal debate of 1560 between Lutheran and Reformed theologians in Heidelberg,[2]: 17 as well as by the fact that the theological faculty which prepared the Catechism consisted of both Reformed and Philippist Lutheran figures.[2]: 18–19 A proponent of this tradition, Lyle D. Bierma, also argues for this by pointing out that the theme of 'comfort' (evident in the famous first Question), is also present in works of Luther and Melanchthon which were significant in the Reformation of the Palatinate.[2]: 21
In its current form, the Heidelberg Catechism consists of 52 sections, called 'Lord's Days', to be taught on each Sunday of the year, and 129 Questions and Answers. After two prefatory Questions (Lord's Day 1), the Catechism is divided into three main parts.[1]: 231
This part consists of the Lord's Day 2, 3, and 4 (Questions 3-11), discussing the following doctrines.
This part consists of Lord's Day 5 through to Lord's Day 31 (Questions 12-85), discussing the following doctrines.
This part consists of the Lord's Day 32 through to Lord's Day 52 (Questions 86-129). It discusses:
The first Lord's Day should be read as a summary of the catechism as a whole. As such, it illustrates the character of this work, which is devotional as well as dogmatic or doctrinal. The celebrated first Question and Answer read thus.
What is thine only comfort in life and in death?That I, with body and soul, both in life and in death, am not my own, but belong to my faithful Saviour Jesus Christ, who with His precious blood has fully satisfied for all my sins, and redeemed me from all the power of the devil; and so preserves me that without the will of my Father in heaven not a hair can fall from my head; yea, and that all things must work together for my salvation. Wherefore by His Holy Spirit He also assures me of eternal life, and makes me heartily willing and ready henceforth to live unto Him.
Bierma argues that the opening lines of this answer are remarkably similar to Luther's explanation of the second article of the Apostles' Creed in hisSmall Catechism (1529), "that I may belong to him [...] [Jesus Christ] has set me free [...] He has purchased and freed me from all sins [...] from the tyranny of the devil [...] with his [...] precious blood". However, the end of the Answer appears to originate in a north German Reformed catechism which was a translation byMarten Micron of a work by Jan Łaski, which states that "the Holy Spirit assures me that I am a member of Christ's church in two ways: by testifying to my spirit that I am a child of God, and by moving me to obey the commandments".[2]: 22
The Catechism is most notoriously and explicitly anti-Roman Catholic in the additions made in its second and third editions to Lord's Day 30 concerning "the popish mass", which is condemned as an "accursed idolatry".
Following the late 17th-centuryWar of Palatine Succession, Heidelberg and the Palatinate were again in an unstable political situation with sectarian battle lines.[10] In 1719, an edition of the Catechism was published in the Palatinate that included Lord's Day 30. The Roman Catholic reaction was so strong, that the Catechism was banned byCharles III Philip, Elector Palatine. This provoked a reaction from Reformed countries, leading to a reversal of the ban.[11]
In some Reformed denominations Question and Answer 80, the first of Lord's Day 30, have been removed or bracketed but noted as part of the original Catechism.[12]

According to W. A. Curtis in hisHistory of Creeds and Confessions of Faith, "No praise is too great for the simplicity of language, the accord with Scripture, the natural order, the theological restraint and devout tone which characterize this Catechism".[1]: 232–233
The influence of the Catechism extended to theWestminster Assembly of Divines who (when restructuring theChurch of England used it as the basis for theirShorter Catechism.[13], which went on the influence thePresbyterian Church in the United States of America. The Catechism is one of thethree Reformed confessions that form the doctrinal basis of the originalReformed Church in The Netherlands, and is recognized as such also by the Dutch Reformed churches that originated from that church during and since the 19th century.
Several Protestant denominations in North America have presently adopted the Catechism officially: theReformed Church in the United States (formerly the German Reformed Church), thePresbyterian Church in America, ECO (A Covenant Order of Evangelical Presbyterians), theChristian Reformed Church, theUnited Reformed Churches, thePresbyterian Church (USA), theReformed Church in America, theCommunion of Reformed Evangelical Churches, theUnited Church of Christ (a successor to the German Reformed churches), ,theEvangelical Association of Reformed and Congregational Christian Churches,[14] theFree Reformed Churches of North America, theHeritage Reformed Congregations, theCanadian and American Reformed Churches,Protestant Reformed Churches, the Reformed Protestant Churches and several other Calvinist churches of Dutch origin around the world. Likewise, the Book of Discipline ofThe United Methodist Church lists it as an influence on United Methodism.
A revision of the catechism was prepared by the Baptist minister Hercules Collins. Published in 1680, under the titleAn Orthodox Catechism, it was identical in content to the Heidelberg catechism, with exception to questions regarding baptism, where adultimmersion was defended against infant baptism and the other modes ofaffusion andaspersion.