Simon Grynaeus (1493 – 1 August 1541) was a German scholar and theologian of the Protestant Reformation.
He was the son of Jacob Gryner, a Swabian peasant, and was born at Veringendorf, in Hohenzollern-Sigmaringen. He adopted the name Grynaeus from the epithet of Apollo in Virgil. He was a schoolmate of Melanchthon at Pforzheim, whence he went to the University of Vienna, distinguishing himself there as a Latinist and Hellenist.
His appointment as rector of a school at Buda was of no long continuance: his views excited the zeal of the Dominicans, and he was thrown into prison. He gained his freedom at the instance of Hungarian magnates, visited Melanchthon at Wittenberg, and in 1524 became professor of Greek at the University of Heidelberg, being in addition professor of Latin from 1526. His Zwinglian view of the Eucharist disturbed his relations with his Catholic colleagues. From 1526, he had corresponded with John Oecolampadius, who in 1529 invited him to Basel, which Erasmus had just left. The university being disorganized, Grynaeus pursued his studies, and in 1531 visited England for research in libraries.
A commendatory letter from Erasmus gained him the good offices of Sir Thomas More. He returned to Basel charged with the task of collecting the opinions of continental reformers on the subject of Henry VIII's divorce, and was present at the death of Oecolampadius (24 November 1531). He now, while holding the chair of Greek, was appointed extraordinary professor of theology, and gave exegetical lectures on the New Testament.