The cultural and artistic legitimacy of photography is recent. For a long time considered merely a tool, it is now regarded in its own right in galleries and museums. It emerged with the rise of metropolises, the monetary economy, industrialization, and democracy; it was, first and foremost, the image of the mercantile society, best equipped to document and update its values. However, while it suited the modern industrial society, today it struggles to meet the needs of an information society based on digital networks. Photography is, therefore, the object of this book: in its plurality and its developments, from the document to contemporary art; in its historicity, from its emergence in the mid-19th century to the current alloy of 'Art-Photography,' which leads André Rouillé to distinguish 'the art of photographers' from 'the photography of artists.