Every few seconds, each of us exhales a rich cocktail of gaseous chemicals into our immediate surroundings. This mixture is quantitatively dominated by nitrogen (74.5 %), oxygen (13.7 %), carbon dioxide (5.3 %) and water vapour (~6 %), but it is the remaining 1 % fraction that earns increasing scientific and medical interest. At these trace levels, exhaled breath is a complex mixture of volatile compounds that derive from internal biochemical processes and can provide potential indications of physiological status, environmental burden, and disease. This lecture will introduce the concept of non-invasive breath analysis as a means for exploring physiological state. After a brief historical overview of detection of disease ‘on the breath’, the talk will introduce state-of-the-art sampling methodologies and analytical technologies, from lab-scale instrumentation to sensor-based devices, and review established breath tests for biomarker detection. The lecture will conclude with a look at current challenges and a prospective outlook of this innovative application in health and disease diagnostics.