Institutes of the Christian Religion (Latin: Institutio Christianae Religionis) is John Calvin's seminal work of systematic theology. Regarded as one of the most influential works of Protestant theology, it was published in Latin in 1536 at the same time as Henry VIII of England's Dissolution of the Monasteries and in his native French language in 1541. The definitive editions appeared in 1559 in Latin and in 1560 in French.

The book was written as an introductory textbook on the Protestant creed for those with some previous knowledge of theology and covered a broad range of theological topics from the doctrines of church and sacraments to justification by faith alone and Christian liberty. It vigorously attacked the teachings of those Calvin considered unorthodox, particularly Roman Catholicism, to which Calvin says he had been "strongly devoted" before his conversion to Protestantism.

The Institutes is a core reference for the system of doctrine adopted by the Reformed churches, usually called Calvinism.

John Calvin was a student of law and then classics at the University of Paris. Around 1533 he became involved in religious controversies and converted to Protestantism, a new Christian reform movement which was persecuted by the Catholic Church in France, forcing him to go into hiding. He moved to Basel, Switzerland for safety in 1535, and around this time he must have begun writing a summary of theology which would become the Institutes. His Catholic opponents sought to tie him and his associates (known as Huguenots in France) to groups of radical Anabaptists, some of which had been put down by persecution. He decided to adapt the work he had been writing to the purpose of defending Protestants suffering from persecution from false accusations that they were espousing radical and heretical doctrines. The work, written in Latin, was published in Basel in March 1536 with a preface addressed to King Francis I of France, entreating him to give the Protestants a hearing rather than continue to persecute them. It is six chapters long, covering the basics of Christian creed using the familiar catechetical structure of the Ten Commandments, the Apostles' Creed, the Lord's Prayer, and the sacraments, as well as a chapter on Christian liberty and political theology. Soon after publishing it, Calvin began his ministry in Geneva, Switzerland.

The Institutes proved instantly popular, with many asking for a revised edition. In 1539, Calvin published a much larger work, with seventeen chapters of about the same length as the six chapters of the first edition. It includes many references to classical authors and Church Fathers, as well as many additional references to the Bible. Calvin's epistle to the reader indicates that the new work is intended for theological students preparing for ministry. Four chapters were added in a third edition in 1543, and a 1550 edition was published with only minor changes. The fifth and final edition with which Calvin was involved, and which is used by scholars as the authoritative text, is 80% larger than the previous edition and was published in Geneva in 1559.

Calvin's theology did not change substantially throughout his life, and so while he expanded and added to the Institutes, he did not change their main ideas.

The Latin word "institutio", translated in the title as "institutes", may also be translated "instruction", as it was in titles of German translations of the work, and was commonly used in the titles of legal works as well as other summary works covering a large body of knowledge. The title of Desiderius Erasmus's Institutio principis Christiani (1516), with which Calvin would have been familiar, is usually translated The Education of a Christian Prince. The form of the short title of the first edition of Calvin's work, published in 1536 is Christianae religionis institutio. The full title of this edition may be translated The Institute of the Christian Religion, Containing almost the Whole Sum of Piety and Whatever It is Necessary to Know in the Doctrine of Salvation. A Work Very Well Worth Reading by All Persons Zealous for Piety, and Lately Published. A Preface to the Most Christian King of France, in Which this Book is Presented to Him as a Confession of Faith. Author, John Calvin, Of Noyon. Basel, MDXXXVI. In the 1539 edition, the title is Institutio Christianae Religionis, possibly to emphasize the fact that this is a new, considerably expanded work. This is followed by "at length truly corresponding to its title", a play on the grandiosity of the title and an indication that the new work better lives up to the expectation created by such a title.

Institutes in its first form was not merely an exposition of Reformation doctrine; it proved the inspiration to a new form of Christian life for many. It is indebted to Martin Luther in the treatment of faith and sacraments, to Martin Bucer in what is said of divine will and predestination, and to the later scholastics for teaching involving unsuspected implications of freedom in the relation of church and state.