Publisher Summary This chapter reviews the current status of shear sensitivity of microorganisms and other biocatalysts. The structural features of biocatalysts serve as a basis for rational explanation of effects of shear damage. One of the key parameters in the development of processes utilizing biocatalysts is their sensitivity to hydrodynamic shear stress. Bioreactors can generate strong forces in the region of the impeller, along the walls, and at air–liquid interfaces. The chapter examines what is known about the sensitivity of enzymes and organisms to shear stress, the magnitude of the forces experienced by biocatalysts in various reactor types, and the implications for the design and operation of biochemical processes It discusses physical and biological mechanisms of shear damage and outlines the ways of overcoming the adverse effects of shear.