Nitric oxide (NO) is a pleiotropic free radical messenger molecule. There is enzymatic, non-enzymatic and bacterial production of NO in the human gut. This book examines the role of NO in human gastrointestinal and hepatic physiology and disease processes. Furthermore, it has long been recognized that nitric oxide is heavily involved in cell signaling. The authors' examine the complex relationship between S-nitrosylation and cancer biology. Other chapters in this book explore the complexity of NO metabolic pathway in order to better understand its role in the interaction between parasites and host cells; the most promising nanomaterials for the development of electrochemically or optical sensors for in vivo NO sensing and the NO pathway in Trypanosoma cruzi epimastigotes, associated with several diseases considered to be public health concerns.