The role of physical transfer processes in bioprocess plants is as important as that of biochemical and microbial processes. Thus, knowledge of the engineering principles of such physical processes is important in the design and operation of bioprocess plants. Although this chapter is intended mainly for nonchemical engineers who are unfamiliar with such principles, it might also be useful to chemical engineering students at the start of their careers. Heat transfer within a homogeneous solid or a perfectly stagnant fluid in the absence of convection and radiation takes place solely by conduction. The transfer of heat and/or mass in turbulent flow occurs mainly by eddy activity, the motion of gross fluid elements that carry heat and/or mass. Transfer by heat conduction and/or molecular diffusion is much smaller compared to that by eddy activity. The film coefficients of mass transfer can be defined similarly to the film coefficient of heat transfer.