Jonathan Alexander professe à l'Institute of Fine Arts de l'Université de New-York. Les médiévistes le connaissent comme éminent spécialiste des manuscrits enluminés, auteur d'ouvrages de référence.
Jonathan J.G. Alexander is the Sherman Fairchild Professor of Fine Arts, Institute of Fine Arts at New York University. His research interests focus on medieval European art, especially manuscript illumination.

On lui doit plusieurs études sur les manuscrits bretons, dont le Harkness Gospels (New York, Public Library 115, IXe s.) [En ligne]
[Description]
et sur un manuscrit de la collection Bradfer-Lawrence:
An Early Breton Gospel Book. A Ninth Century Manuscript from the Collection of H. L. Bradfer-Lawrence (1887-1965), Cambridge: Printed for presentation to the members of the Roxburghe Club, 1977 (avec Francis Wormald)

Autres ouvrages
Studies in Italian Manuscript Illumination, Pindar Press, 2002.
The Painted Page: Italian Renaissance Book Illumination 1450-1550, ed. and contributor, Prestel, 1994.
Medieval Illuminators and Their Methods of Work, Yale University Press, 1993.
Age of Chivalry: Art in Plantagenet England 1200-1400, ed. with Paul Binski, Royal Academy of Arts in association with Weidenfeld and Nicolson, 1987.
Insular Manuscripts 6th - 9th Century, Harvey Miller, 1978