Most commercial process control tools and techniques used in the chemical process industries are applicable to bioprocesses (e.g. processes that make certain medicines). While bioprocesses include several different unit operations, the focus of most of this paper will be the control of bioreactors (i.e. fermentors) in which a near optimal environment is desired for microorganisms to grow, multiply, and produce a desired product. Bioreactor control provides special challenges due to significant process variability, the complexity of biological systems, the need, in many cases, to operate in a sterile environment, and the relatively few real-time direct measurements available that help define the state of the culture. This has led to some creative solutions as well as the identification of topics where further research and development and vendor software functionality are needed. (c) 2006 Elsevier Ltd. All rights reserved.