The area of chemical engineering which has become known as Process Systems Engineering developed initially out of the availability of a tool, the high-speed digital computer. Coincidentally, 50 years ago, computers appeared for the first time, and as they became more generally available and useful, chemical engineers were amongst the first to recognise and exploit their potential for large scale calculations. Most of the efforts of early process systems engineers were focused on circumventing the limitations of early computers, particularly their lack of speed and of storage capacity to handle the very large problems whose solution was an ultimate aim. Over the last few years these constraints have practically vanished. However, some of the discipline’s most important long-term achievements have come in the form of a better understanding of large-scale concepts; these have resulted from the need to analyse and decompose problems and procedures so that they might be accessible to computing machines of limited capacity. This has also made them more accessible to we human computing machines of likewise limited capability. The first half century of process systems engineering was dominated by mathematics. Over the next half century, mathematics will be taken for granted, and emphasis will shift to information and understanding : how it can be represented, captured, accessed, transferred and exploited. The ability to perform very large numerical calculations in a simple and routine manner will encapsulate the mathematical achievements of the last 50 years and make them accessible to all chemical engineers. Future research can thus concentrate on new areas. The current ready availability of computers is already having a major effect on the way in which all chemical engineers and scientists work. In the future, computers will become not just available, but ubiquitous, providing instantaneous access to the sophisticated mathematical and informatic tools which have been and will be developed. It is difficult to predict the impact of this ubiquity, and any prediction is likely to be an underestimate. Still harder to assess are the consequences of not just the power and ubiquity of computer tools, but their connectivity. This will provide fast, worldwide connection between computer software and computer users on an unprecedented scale, and seems likely to create a qualitative change in the way in which engineers will use creatively their expanding range of powerful tools.