France, is supposed to have been present at the Council of Kiersy in 840, as deacon of Laon. After the death of Theutbalde, Wulfade seized the bishopric of Langres in spite of all opposing canons; but Hincmar, archbishop of Rheims, declared against him, and Charles the Bald compelled him to flee. Hilduin, lay abbot of St. Denis, then proposed Isaac as bishop, and by his influence caused him to be appointed. Isaac was ordained bishop of Langres about 856. We afterwards find his name in the councils of Toul and Langres (859), of Tousy (860), of Pistes (862), of Verberie, and of Soissons (866) — an evidence that he had gained great consideration and influence. His mildness caused him to be surnamed bonus, and the martyrology of the Church of Dijon praises him highly. A lasting monument of his efforts to effect a reform among the monastic orders is his work on Canons, published by Sirmond, Conciles, vol. 3; Labbe, Concil. etc.; Baluze, Capitdlaires, vol. 2. See Gallia Christ. vol. 5, col. 533; Hist. Litt. de la France, 5, 528; Hoefer, Nouv. Biog. Generale, 26:4. (J. N. P.)