Sebastian Franck (20 January 1499 – c. 1543) was a 16th-century German freethinker, humanist, and radical reformer.
Franck was born in 1499 in Donauwörth, Bavaria. Because of this he styled himself Franck von Word. He entered the University of Ingolstadt on 26 March 1515, and afterwards went to Bethlehem College, incorporated with the university, as an institution of the Dominicans at Heidelberg. Here he met Martin Bucer and Martin Frecht, with whom he might have attended Luther's Heidelberg disputation in October 1518.
Originally ordained as a priest, in 1525 Franck went over to the Reformed party at Nuremberg and became preacher at Gustenfelden. His first work was a German translation (with additions) of the first part of the Diallage (or Conciliatio locorum Scripturae), directed against Sacramentarians and Anabaptists by Andrew Althamer, then deacon of St. Sebald at Nuremberg. On 17 March 1528 he married Ottilie Beham, supposedly the sister of the "godless" painters, Bartholomew and Sebald Beham, pupils of Albrecht Dürer and followers of Hans Denck. In the same year he wrote a treatise against drunkenness. In 1529 he produced a free version of the Supplycacyon of the Beggers, written by the English Protestant Simon Fish. Franck, in his preface, says the original was in English; elsewhere he says it was in Latin; the theory that his German was really the original is not warranted.