An expert system (ES) is a problem-solving package that mimics a human expert in a specialized problem area. Several ESs have already been successfully implemented in production and operations management (P/OM), and many more are being developed. Though P/OM is a promising area for ESs, applications to date have been haphazard and independent research efforts to produce customized designs. ESs in P/OM can be classified using a two-dimensional framework that separates strategically and tactically oriented applications on one dimension, and operations and resources on the other. We group ESs according to this two-dimensional framework and also indicate the knowledge representation scheme, reasoning, and system building tool or programming language used.