The purpose of the paper is to demonstrate aspects of control for biotechnological processes, to introduce both the control engineer and the chemical engineer or biologist to this interdisciplinary field. Starting with an analysis of aspects and problems which arise during automation of biotechnical processes, some of the modern control principles are presented and the perspectives of their use in control of fermentations are discussed. The methods have been known for years, and theoretical research on most of these may be assumed to be complete; however, the availability of inexpensive microcomputers during recent years has also enabled an economical application for small plants. Moreover, the presented algorithms may be used for the optimal design of reactors and plants.