KeyWords: telephone call center, contact center, tele-services, tele-queues, capacity management, staffing, hiring, workforce management systems, ACD reports, queueing, Erlang C, Erlang B, Erlang A, QED regime, time-varying queues, call routing, skills-based routing, forecasting, data mining.

We characterize the state of research on telephone call centers. We begin with a tutorial on how call centers function and proceed to survey academic research devoted to the management of their operations. We then outline important problems that have not been addressed and identify promising directions for future research.