Most production processes in biotechnology are now carried out in fed-batch operation. Bioreactors, which are mainly used in these fed-batch processes, are the aerated stirred tank and the bubble column. They only compete with each other in large production plants, so the focus here is on the large reactors. These bioreactors are now designed and operated using model-based methods. The models link the kinetic properties of the cells with the transport properties of the reactors. From an engineer’s perspective, their transport properties are of primary interest. Here, the most important practical aspects of bubble columns and stirred tank bioreactors are highlighted. Both types of reactors are illustrated with specific examples from industry.