Hans Arp (1886-1966) can justly be called the father of twentieth-century abstract sculpture, an artist whose impact traversed countless early modernist avant-gardes, from Dada and Surrealism to Concrete art. Arp's sculptures, in all their wondrous morphous plasticity, lend themselves ideally to such varied assimilation, and also--less happily--to forgery. In recent years, some controversy has arisen as to the authenticity of several Arp works, as a number of imitations have circulated in the art market. This substantial publication, undertaken by the independent scholars Arie Hartog and Kai Fischer, decisively counters the problem by assembling all of the authenticated examples of every one of Arp's known sculptures and bringing their respective status up to date. An introductory essay describes the posthumous history of Hans Arp's oeuvre.