Body-on-a-chip (BOC) systems consists of multiple microscale models of different human organ (physiologically scaled to one another) that are physically connected located on a synthetic "chip" format and connected to each other using a microfluidic system, thus emulating the circulatory system within the body. Simpler versions of these systems, known as Organ-on-a-chip (OOC) consists of one organ per chip and have been an emerging area of interest since the past 13-15 years as in vitro biomimetic systems for predicting physiological response to drugs and chemicals. Although animal models have been the gold standards for preclinical drug testing, animal models often do not predict human response effectively; thus, increasing the demand for more advanced in vitro human tissue/ organ model platforms. Since, BOC systems can recapitulate native tissue/ organ architecture, diffusion kinetics of drugs physiological flow conditions etc., similar to what would happen in the body, they are particularly powerful in predicting human efficacy prior to clinical testing of a drug, determining potential toxicity, or in clinical studies to test underlying mechanisms or action or adverse effects. With recent advancements in high-throughput analysis systems and artificial intelligence, it has also become possible to screen several drugs at a time, thus significantly speeding up discovery, development and testing of pharmacologically useful compounds and reducing costs. Now BOC systems are also finding applications in evaluating the safety of chemicals, cosmetics, food ingredients, and also in life science research. Body-on-a-chip: Essentials and Applications provides the reader high quality information, in a single resource, necessary to explore the use of BOC systems from design and development to testing and personalized medicine, to medical research and diagnostics.