What is air? You don't think about air or even perceive it unless it has changed from its usual state. Air, that most ubiquitous of the four elements, was long the most inexplicable enigma, peopled by gods and their messengers, venerated as the abode of spirits or demons. Nowadays air has been deconsecrated' and almost entirely demystified by science. Its availability is crucial; it envelops us and our planet allows us to breathe and is anything but something to be taken for granted.Humanity has always been preoccupied with air as a medium, also in the artistic sense. During the 20th century the approach to this theme was deepened in so far as air was not merely represented in visual terms, but was deliberately used by architects, designers and artists as a material. What is air? This book tries to unite culture, art and science. From an anthropocentric perspective, this work examines the topic across a broad range of sciences and disciplines, from antiquity to today.