It has been a pleasure to edit this special issue on process intensification (PI), a topic that is attracting much attention from industry as well as academia. Process systems engineering (PSE) has been closely related to the developments within PI and this special issue of Computers and Chemical Engineering has collected papers from invited authors covering a wide range of topics within PI. We include the idea of any process design feature that retains the primary process objectives (production rate and fitness-for-use criteria) while also improving one or more performance parameters which could include economics (raw material consumption, energy requirement, labor requirement, other operating costs, equipment capital, working capital, etc.), environmental impacts, physical plant size, employment, flexibility, controllability, robustness, reliability, safety, etc. Topics covering synthesis issues, modelling issues, design issues, analysis issues, new application examples, process improvement, etc. are included in this special issue.