The Institutes of Christian Religion is a foundational text of Protestant theology written by John Calvin, first published in 1536. This work systematically outlines Calvin's beliefs about salvation, the nature of God, and the role of the Church, playing a crucial role in shaping Reformed theology and influencing the Protestant Reformation. Its ideas challenged existing Catholic doctrine and promoted the principles of predestination and justification by faith, which resonated with the religious and political changes in 16th-century Europe.