Protestantism in France has existed in its various forms, starting with Calvinism and Lutheranism since the Protestant Reformation. John Calvin was a Frenchman, as were numerous other Protestant Reformers including William Farel, Pierre Viret and Theodore Beza, who was Calvin's successor in Geneva. Peter Waldo (Pierre Vaudes/de Vaux) was a merchant from Lyon, who founded a pre-Protestant group, the Waldensians. Martin Bucer was born a German in Alsace, which historically belonged to the Holy Roman Empire, but now belongs to France.
Hans J. Hillerbrand in his Encyclopedia of Protestantism claims the Huguenots reached as much as 15% of the French population on the eve of the St. Bartholomew's Day massacre, declining to 10-12% by the end of the 16th century, and further after heavy persecution began once again with the revocation of the Edict of Nantes by Louis XIV.