Process systems engineering (PSE) has been an active research field for almost 50 years. Its major achievements include methodologies and tools to support process modeling, simulation and optimization (MSO). Mature, commercially available technologies have been penetrating all fields of chemical engineering in academia as well as in industrial practice. MSO technologies have become a commodity, they are not a distinguishing feature of the PSE field any more. Consequently. PSE has to reassess and to reposition its future research agenda. Emphasis should be put on model-based applications in all PSE domains including product and process design, control and operations. Furthermore, systems thinking and systems problem solving have to be prioritized rather than the mere application of computational problem solving methods. This essay reflects on the past, present and future of PSE from an academic and industrial point of view. It redefines PSE as an active and future-proof research field which can play an active role in providing enabling technologies for product and process innovations in the chemical industries and beyond. (C) 2008 Elsevier Ltd. All rights reserved.