What is photography? What, if it exists, is its own “genius”? What relationship has it had, and does it have, with the other arts, and above all with what it represents, with its own referent? Many have been the questions surrounding the nature of photography and its functions, many the overall investigations into its individual historical phases. This work, first published in 1937, was long meditated upon afterwards, and in 1982 appeared, edited by the Museum of Modern Art in New York, in a completely revised and enriched new edition, featuring important figures of photographers discovered only in recent decades. A peculiarity of the book is that it avoids ontological problems and partial analyses in order to reconstruct the path, from the origins to today, of an independent art form, evaluating technique and image as inseparable complementary parts of the result: the daguerreotype, printing and developing papers, portable cameras and the Polaroid, rayographs are examined in close connection with the questions of the diffusion and functions of the photographic medium, from amateurism to the snapshot, from artistic to documentary photography, to abstract experiments.