This book integrates the research progress of Tryptophan (Trp) and its metabolites in animal nutrition and human health. It recapitulates the effects of Trp nutrition on the regulation of various physiological functions in farmed animals as well as the clinical connections between Trp metabolism and human diseases. Furthermore, this book includes detailed information about the manufacturing process of industrial Trp production and methodologies to study Trp metabolism. This book not only brings numerous benefits to academic communities worldwide but also provides practical values for industrial professionals/companies. Both of these two aspects will expand our understanding of how amino acid metabolism contributes to the maintenance of host health.