The term organ on a chip is used to describe the latest stage of development of in vitro cell culture technology. Figure 26.1 shows its steady development since the 1960s. Each step forward has improved our ability to model human-clinical response to new drugs or therapies and has enabled safety risk assessment of existing cosmetics, personal care products, or other chemicals in the environment. Scientific evidence that the predictive power of in vitro tests is superior to the use of animals will trigger a major shift in the way that medical research, in many areas, is carried out. In this emerging field, some researchers also refer to organ on a chip as a microphysiological system. As yet, there are few agreed upon standards or definitions for the latest developments