In 1979, he joined the Mathematics Center at Bell Laboratories where he stayed until his retirement as a Distinguished Member of Technical Staff 20 years later.
He published 4 graduate-level text books, and papers in the proceedings of some 250 conferences and workshops, most of these being preliminary versions of journal articles.
The processes studied include those in the theories of scheduling, bin packing, sequential selection, graphs, and dynamic allocation, along with those in queueing, polling, reservation, moving-server, networking, and distributed local-rule systems (e.g. cellular automata).
His contributions have been divided between mathematical foundations and the design and analysis of approximation algorithms providing the basis for engineering solutions to NP-hard problems.
[1] Coffman has been active professionally serving on several editorial boards, dozens of technical program committees, setting research agendas in workshops of the National Research Council, co-founding the Symposium on Operating Systems Principles, and the special interest groups on performance evaluation of both ACM and IFIPS.