Volatile biomarkers play a significant signalling role in communication between biological cells living as individual entities or as mini-societies that sense, respond and adapt to changes in their environment. In this process, volatile biomarkers can leak into the blood, from which they can be secreted into most body fluids (blood, breath, skin, urine, saliva, feces, etc.), from which sensing devices can capture and interpret their chemical fingerprint to reflect any association with health disorders in a fast, easy, and minimally non-invasive manner. This book introduces the concept of biomarkers within the body in terms of basic and translational sciences. It starts with a comprehensive review of the expression and mechanistic pathways involving volatile biomarkers at single cell and (micro)organism levels, cell-to-cell and cell-to-organism communications, and their secretion into body fluids. It discusses several ways for discovering and detecting the secreted biomarkers using mass spectrometry and other spectroscopic techniques. This is followed by an appraisal and translation of the accumulating knowledge from the laboratory to the Point-of-Care phase, using selective sensors as well as desktop and wearable artificial sensing devices, e.g., electronic noses and electronic skins, in conjugation with AI-assisted data processing and healthcare decision-making in diagnostics. The book offers an outlook into the challenges in the continuing development of volatile biomarkers and their wider availability to healthcare, which can be substantially improved. It should appeal to research groups in universities, start-up and large-scale industries associated in all aspects of biomedicine.