He was a prolific contributor to both fields for six decades, having authored or coauthored several dozen research papers and monographs.

His students include Aldridge K. Bousfield, William Dwyer, Stewart Priddy, Emmanuel Dror Farjoun, and Jeffrey H. Smith.

He was an emeritus professor at the Massachusetts Institute of Technology where he taught from 1959, formally retiring in 1993.

He played a role in the beginnings of modern homotopy theory similar to that of Saunders Mac Lane in homological algebra, namely the adroit and persistent application of categorical methods.

His most famous work is the abstract formulation of the discovery of adjoint functors, which dates from 1958.