The Foundation-Book (official title: A Foundation and Plain Instruction of the Saving Doctrine of Our Lord Jesus Christ) is Menno's most important work. In its importance for the Mennonites it is sometimes compared to John Calvin's Institutes for the reformed church. Menno's Foundation-Book was published in 1539 and deals with subjects such as 'The Time of Grace', 'True Repentance', 'Concerning Faith', 'The Apostolic Baptism', 'The Lord's Supper', 'Separation From the World', and 'The True Ministers'. After the disaster at Münster, the Foundation-Book became the most important guide book for the 'sheep without a shepherd', the true, peaceful anabaptists in the Netherlands.
The Foundation-Book was intended as a defense against the many misunderstandings about Anabaptist ideas. Menno says he wrote it "out of a desire to be of service to all men, whoever they may be, for their salvation". As the Dutch historian H.W. Meihuizen wrote in his introduction to a new edition of the Foundation-book in 1967: 'It is a book written with emotion; it presents to us a man of flesh and blood who intended to bring more a vision than a treatise, more an ideal than a system; and it could well be that the vision and ideal, in spite of the antiquated form in which they are contained, are still able to speak to our time.'
The only known copies of the first edition of 1539 can be found at the Library of the Verenigde Doopsgezinde Gemeente in Amsterdam (two copies), the University Library of Amsterdam, the Koninklijke Bibliotheek (Royal Library) in The Hague, the British Museum in London, and the Stadtbibliothek (Municipal Library) in Hamburg.
Subsequent editions were published around 1554, probably in Lübeck or Wüstenfelde, and in 1558. This latter edition had a new title: Ein Fundament unde klare awisinge van de heylsame unde Godtfellyghe leere Jesu Christi uth Godes woort mit gueder corte vervatet under wederumme mit grooter vlyte averghelesen unde ghebetert (A Foundation and Plain Instruction of the Saving and God-Pleasing Teaching of Jesus Christ, Briefly Compiled from the Word of God and Again with Great Diligence Read Over and Improved).
The 1558 edition had the following new books added to it:
- Concerning the True Christian Faith
- Concerning Regeneration or the New Creature
- A Consolation Regarding Suffering, the Cross, and the Persecution of the Saints
- Meditation on the Twenty-Fifth Psalm
- Concerning the Spiritual Resurrection
- Concerning Excommunication, Ban, and Avoidance
- How Pious Parents Should Train Their Children
This enlarged edition was frequently reprinted, translated into German (appearing first in 1575) and eventually incorporated into the complete works of Menno Simons. All American editions of the Foundation-Book are based on the edition of 1558.
In 1616 a new edition was published under the title Dat Fundament der Christlycken Leere. Door Menno Simons op dat alder correckste geschreven/ ende wtghegheven / Anno M.D.XXXIX. Ende nu nae het alder outste exemplaer wederom herdruckt / Anno 1616. It was probably published by followers of Menno.