The history of the fouling of heat transfer surfaces is reviewed up to 1979. Four epochs of fouling are identified. Particular attention is paid to fouling in steam boilers and steam condensers. The origin of the cleanliness factor and the fouling factor are discussed. The introduction of scientific methods of studying fouling through the model of Kern and Seaton, and the application of models based on fundamental ideas in mass transfer are considered. The paper concludes by drawing attention to the successes in understanding fouling and pointing out the needs for future research.