The problems caused by fouling are outlined, and recent work to understand the processes of fouling reviewed. Fouling is a two‐stage process: the reactions governing the first stage are unclear, but the second stage appears to be governed by protein aggregation in the bulk fluid. The use of a computer model for fouling in simulating heat exchanger behaviour is described: it is possible to select an exchanger with an optimal fouling response. The need for accurate fouling and cleaning kinetics is stressed, and the role of a process monitor outline