Abstract Mixing and aeration are normally used to provide a homogeneous, suitable environment for cells in a bioreactor. In spite of the large cumulative experience in the use of bioreactors in the biotechnology industry, there are still challenges when scaling‐up animal cell cultures. Remarkable advances have been achieved over the last two decades in designing and applying mixing and aeration strategies, as well as understanding the effects of hydrodynamic forces on cell cultures. This section reviews the basic concepts and current practices for mixing and aeration in bioreactors, with focus on stirred tank bioreactors (STR), as most of the processes for recombinant proteins, antibodies, and vaccines involve the use of STR. Current methods of oxygen supply in STR include surface aeration and gas sparging, although the use of perfluorocarbons, oxygen carriers and membranes has been investigated. Sparger design and the role of CO 2 accumulation and removal are discussed. Also, a summary of the main aspects involved in mixing is presented, including tank characteristics, impeller geometry, and power drawn. Finally, this review explores several different approaches that have been taken in order to unveil the response of animal cells to the hydrodynamic forces generated inside bioprocessing devices.