Casaubon, Isaac, one of the most learned men of his own or of any age, was born Feb. 18th, 1559, at Geneva, whither his family, originally of Dauphiné, fled to avoid the persecutions to which the French Protestants were exposed. His father, Arnauld Casaubon, a minister of the Reformed Church, returned into France, and devoted himself to the education of his son, who, at nine years of age, spoke Latin. In 1578 he went to Lausanne, and studied law, theology, and the Greek and Oriental languages. He soon became professor of Greek at Geneva, and married the daughter of Henry Stephens, the celebrated printer, and soon began to put forth translations of the Greek and Latin writers, with notes and commentaries. In 1596 he accepted the Greek professorship at Montpellier, but held it only until 1599, when he was called to Paris by Henry IV, and received the appointment of librarian to the king. Henry appointed him one of the Protestant judges in the controversy between Du Perron, bishop of Evreux, and Du Plessis Mornay, at Fontainebleau (1600). The Roman Catholics made many attempts to gain so distinguished a convert; but there does not seem to be any reason for concluding that they had even partial success, although it was given out that he had wavered in a conference with Du Perron. On the death of Henry IV, 1610, Casaubon went to England with Sir Henry Wotton. James I received him with distinction, and presented him, though a layman, to a prebend at Canterbury, and (it is said) to another in the church of St. Peter, at Westminster. He died July 1, 1614, and was buried in Westminster Abbey. Besides his classical works he published Exercitationes contra Baronium (London, 1614, fol., Frankfort, 1615, and Geneva, 1663, 4to); Novum Testamentum Graecum (Geneva, 1587, 16mo, with notes; reprinted in the Critici Sacri); De libertate Ecclesiasticâ (1607, 8vo), undertaken by order of Henry IV on occasion of the difference between the republic of Venice and Pope Paul V, with the aim to maintain the rights of the temporal power against the court of Rome. It was stopped by the king's order, when the difference in question was settled. He also wrote Ad Frontonern Ducaeum Epistola (Lond. 1611, 4to) against the Jesuitical doctrine of authority. The best edition of his Letters is that of Rotterdam (1709, fol). There is a full account of his life and writings in Haag, La France Protestante, 3:230. — Biog. Univ. 7:259; Landon, Eccl. Dictionary, s.v.; Hoefer, Vouv. Biog. Generale, 8:954.