The Dutch reformer Menno Simons (ca. 1496-1561) was one of the prominent leaders of Anabaptism in the Netherlands and northern Germany during one of the movement's most difficult periods.

Menno Simons was born in the village of Witmarsum in Dutch Friesland. Nothing is known of his early background, except that he decided to become a Catholic priest and was consequently ordained in March 1524. In his new capacity, he served from 1524 to 1536 near and in his native village. His work as a priest, however, was troubled by doubts, beginning as early as 1525, about the validity of Catholic teachings. Influenced by the writings of the Protestant reformers, especially Martin Luther, and by his own reading of the Bible, he finally decided in 1536 to renounce the Catholic Church and to be baptized as an Anabaptist. In the following year, he was ordained to the office of a bishop, or overseer, of the Anabaptists.

Since the Anabaptists were considered radical revolutionaries and were being persecuted (especially after the events in Münster, Westphalia, under John of Leiden) by the other religious groups, the office was not particularly desirable. In this position, Menno preached his nonviolent type of Anabaptism in the Netherlands until 1544, by which time he had become a much pursued heretic. After 1544 he spent most of his time in Germany, first along the Rhine and then later in the north. All the while he continued to serve on behalf of his faith until his death on Jan. 31, 1561. His constant activity made possible the survival and spread of the original, peaceful Anabaptist movement when it was most threatened by persecution.

During all of his missionary activity, Menno also wrote numerous pamphlets and books explaining the Anabaptist doctrines. The most important one was Foundation of the Christian Doctrine, or Foundation Book (1539). Although Menno was not a great theologian or philosopher, his writings were buttressed with quotations from Scripture and provided his followers, called Mennonites, with a good understanding of basic Anabaptist concepts. He believed that baptism and the Lord's Supper did not confer grace but reflected the inward state of the believer. The true church was composed of those who had experienced regeneration and a "new birth," thus rejecting infant baptism. Although oaths and military and government service were forbidden as contrary to Scripture, magistrates were to be obeyed in everything not prohibited by Scripture.