This crucial history explores the role of philosophical thought in transforming the way that artwork emerging from mental hospitals in the early 20th century was treated. At first seen purely as a documentation of patients' symptoms, these expressions of creativity and often resistance gradually came to be assessed as art objects in their own right. Howard Caygill plots the philosophical re-evaluation of the art of the mentally ill, from the reforms in psychiatric classification at the turn of the 19th century to the new aesthetic categories of Art Brut, Art Fou, and Artaud's theatre of cruelty some fifty years later. Shifting focus from the work of the 'illustrious mad' like August Strindberg and Friedrich Nietzsche to the outpouring of work by anonymous patients shows how philosophy responded to the challenge that these artworks posed to the existing aesthetic structures. While this period of unprecedented creative output from an unfamiliar source reshaped ideas of resistance and authenticity in art, it was relatively short-lived. The book concludes with Foucault's and Heidegger's visits to the asylums at Munsterlingen, Bellevue and Zollikon in the 1950s, as the advent of increasingly pharmacological treatment marked the end of what had become known as 'mad art'.