Architecture & Academe: College Buildings in New England before 1860 (Find It @ Harvard) by Bryant F. Tolles, Jr. Lebanon, NH: University Press of New England, 2011. 

"The Architecture of American Colleges; I. Harvard" by Montgomery Schuyler. Architectural Record, Volume XXVI (July-December 1909): 243-269.

"The art of architecture: Harvard's campus reflects three centuries of architectural history" by Colleen Walsh. Harvard Gazette February 16, 2011. 

Cambridge Buildings and Architects compiled by Christopher Hail. Cambridge, Mass.: [C. Hail], 2001.
Database lists all buildings (that the compiler has been able to identify) past and present, organized by street address. Building histories include dates, type of structure, architects of original structure and of subsequent modifications, sources of information (building permits, COPAR survey, etc.), links to color photographs of selected buildings.

"Early College Buildings at Cambridge" by Andrew McFarland Davis. Proceedings of the American Antiquarian Society, New Series, Volume VI (April 1890): 323-349.

Education, Bricks and Mortar: Harvard Buildings and Their Contribution to the Advancement of Learning. Cambridge: The University, 1949. 

Harvard: An Architectural History (Find It @ Harvard) by Bainbridge Bunting. Cambridge: Harvard University Press, 1985.

Harvard and Its Surroundings by Moses King. Cambridge: Moses King, Publisher, 1884.

Harvard University: A Selection of Historic Buildings (Find It @ Harvard). Cambridge: Harvard University Press, 1986. 

Harvard University : An Architectural Tour (Find It @ Harvard) by Douglass Shand-Tucci. Photographs by Richard Cheek; foreword by Neil L. Rudenstine. New York: Princeton Architectural Press, 2001.

Harvard University Handbook: An Official Guide to the grounds, buildings, libraries, museums, and laboratories, with notes on the history, development and activities of all departments of the University. Cambridge: Harvard University Press, 1936. 

Survey of Architectural History in Cambridge. Report 2, Mid Cambridge. Report 4, Old Cambridge (Find It @ Harvard) by the Cambridge Historical Commission. Cambridge: Distributed by M.I.T. Press, 1967, 1973. 

Views of Harvard: A Pictorial Record to 1860 (Find It @ Harvard) by Hamilton Vaughan Bail. Cambridge: Harvard University Press, 1949. 

"Views of Harvard to 1860: An Iconographic Study," by Hamilton Vaughan Bail. This version appeared in seven parts in the Harvard Library Bulletin, 1947-1949:

Part IHLB Volume I Number 1 (Winter 1947): 11-28 
Part II: HLB Volume I Number 2 (Spring 1947): 185-211 
Part III: HLB Volume I Number 3 (Autumn 1947): 339-376 
Part IV: HLB Volume II Number 1 (Winter 1948): 44-82 
Part V: HLB Volume II Number 2 (Spring 1948): 179-221 
Part VI: HLB Volume II Number 3 (Autumn 1948): 309-343 
Part VII: HLB Volume III Number 1 (Winter 1949): 44-93