The purpose of this review is three-fold. First, sketch the directions that research and industrial applications of "intelligent systems" have taken in several areas of process engineering. Second, identify the emerging trends in each area, as well as the common threads that cut across several domains of inquiry. Third, stipulate research and development themes of significant importance for the future evolution of "intelligent systems" in process engineering. The paper covers the following seven areas : diagnosis of process operations; monitoring and analysis of process trends; intelligent control; heuristics and logic in planning and scheduling of process operations; modeling languages, simulation, and reasoning; intelligence in scientific computing; knowledge-based engineering design. Certain trends seem to be common and will (in all likelihood) characterize the nature of the future deployment of "intelligent systems". These trends are : (1) Specialization to narrowly defined classes of problems. (2) Integration of multiple knowledge representations, so that all of relevant knowledge is captured and utilized. (3) Integration of processing methodologies, which tends to blur the past sharp distinctions between AI-based techniques and those from operations research, systems and control theory, probability and statistics. (4) Rapidly expanding range of industrial applications with significant increase in the scope of engineering tasks and size of problems.