This is a Print On Demand Publication. Contents: Introduction; The Life of Abbot Joachim; The Structure and Purpose of the “Liber de Concordia”; The Date of the “Liber de Concordia”; The Tables and Figures; The Two “Diffinitiones”; The Manuscripts of the “Liber de Concordia”; The Manuscript Families of the “Liber de Concordia”; The Letter of Pope Clement III and the Testamentary Letter; and Ratio editionis”. The Text: The Letter of Pope Clement III; The Testamentary Letter of Abbot Joachim; and The “Liber de Concordia”: Preface and Books One, Two, Three and Four. Glossary and Bibliography. Illustrations.