James Lainez (1512 - 1565) was a Jesuit General and theologian.

Born in Almazon , Spain, Lainez came from a Catholic family that had once been Jewish. He graduated from the University of Alcalà , and then continued his studies in Paris, where he came under the influence of Ignatius of Loyola. He was one of the seven men who, with Loyola, formed the original Society of Jesus in 1534.

He spent his early years as a Jesuit in Italy, where his preaching was thought to have convinced great numbers of people to reject Protestantism. Pope Paul III sent him as his representative, along with another Jesuit, to the Council of Trent. Persuaded by his arguments, the Council fathers condemned the Lutheran position on justification by faith alone. He played an important role in many of the sessions of this ecumenical council, which lasted for eighteen years.

After the death of Ignatius he became the second general of the Jesuits, in 1558. On the death of Pope Paul IV, many cardinals wished to elect Lainez pope, but he fled from them in order to avoid this fate.

Lainez retired to Rome at the conclusion of the Council of Trent and died two years later.

Several spellings of his names (James, Jacob; Laines, Laynez, Lainez) are in use and some of them can be found in other Wikipedia articles.