The combination of cell culture models with microscale technology has fostered emergence of in vitro cell-based microphysiological models, also known as organ-on-a-chip systems. Body-on-a-chip (BOC) systems, which are multiorgan systems on a chip to mimic physiological relations, enable recapitulation of organ–organ interactions and potentially whole-body response to drugs, as well as serve as models of diseases. Chemical reaction engineering principles can be applied to understanding complex reactions inside the cell or human body, which can be treated as a multireactor system. These systems use physiologically based pharmacokinetic models to guide the development of microscale systems of the body where organs or tissues are represented by living cells or tissues, and integrated into BOC systems. Here, we provide a brief overview on the concept of chemical reaction engineering and how its principles can be applied to understanding and predicting the behavior of BOC systems.