After several years studying law, Calvin began to study theology and classical literature in 1531, by which time he had already been exposed to (and converted by) the Protestant thought of Luther. In the 1530s he published a series of important biblical commentaries and agitated for reform of the church, which led to his exile to Basel, Switzerland, in 1535. There he produced the first small edition of his most important work, the Institutes of the Christian Religion (1536), to which he added material throughout his life. It was there that Calvin developed the idea that proved most influential to subsequent Protestant thought, the doctrine of predestination.
In 1536 Calvin settled in Geneva, where he remained for two years, again advocating church reform. He was expelled in 1538, but returned in 1541 and remained for the rest of his life. By 1555 he was the most powerful figure in the city, making Geneva a home for Protestant refugees and a center for Protestant thought.