John Calvin (1509–1564) was born in Noyon in northwestern France. As a young man he studied law, which had a decisive impact on his mind and later his thought. In 1533, he experienced a religious crisis, and as a result converted to Protestantism.

Calvin believed that God had specifically selected him to reform the church. Accordingly, he accepted an invitation to assist in the reformation of the city of Geneva. There, beginning in 1541, Calvin worked assiduously to establish a well-disciplined Christian society in which church and state acted together.

To understand Calvin’s Geneva, it is necessary to understand Calvin’s ideas. These he embodied in The Institutes of the Christian Religion, published first in 1536 and in its final form in 1559. The cornerstone of Calvin’s theology was his belief in the absolute sovereignty and omnipotence of God and the total weakness of humanity. Before the infinite power of God, he asserted, men and women are as insignificant as grains of sand.

Calvin did not ascribe free will to human beings because that would detract from the sovereignty of God. Men and women cannot actively work to achieve salvation; rather, God in his infinite wisdom decided at the beginning of time who would be saved and who would be damned. This viewpoint constitutes the theological principle called predestination. Many people consider the doctrine of predestination, which dates back to Saint Augustine and Saint Paul, to be a pessimistic view of the nature of God. But “this terrible decree,” as even Calvin called it, did not lead to pessimism or fatalism. Instead, many Calvinists came to believe that, although one’s own actions could do nothing to change one’s fate, hard work, thrift, and proper moral conduct could serve as signs that one was among the “elect” chosen for salvation.

Calvin transformed Geneva into a community based on his religious principles. The most powerful organization in the city became the Consistory, a group of laymen and pastors charged with investigating and disciplining deviations from proper doctrine and conduct.

Serious crimes and heresy were handled by the civil authorities, which, with the Consistory’s approval, sometimes used torture to extract confessions. Between 1542 and 1546 alone, seventy-six persons were banished from Geneva, and fifty-eight were executed for heresy, adultery, blasphemy, and witchcraft (see "The Great European Witch-Hunt").

Geneva became the model of a Christian community for many Protestant reformers. Religious refugees from France, England, Spain, Scotland, and Italy visited Calvin’s Geneva. Subsequently, the church of Calvin — often termed “Reformed” — served as the model for the Presbyterian Church in Scotland, the Huguenot Church in France, and the Puritan churches in England and New England.

Calvinism became the compelling force in international Protestantism. Calvinists believed that any occupation could be a God-given calling and should be carried out with diligence and dedication. This doctrine encouraged an aggressive, vigorous activism in both work and religious life, and Calvinism became the most dynamic force in sixteenth- and seventeenth-century Protestantism.