Prosper-Alphonse Isaac was a French engraver.

Originally from Calais, Isaac was the son of a lace manufacturer. He moved to Paris in the late 1870s and wanted to become a painter, so he took classes with Jean-Paul Laurens.

He intervened to ensure that Rodin was commissioned to create Les Bourgeois de Calais and joined a group of Parisians interested in Japanese art, building up a fine personal collection in just a few years. The influence of Japan led him to abandon painting and produce dyed fabrics, which were highly successful.

He began engraving in 1900, using drypoint, aquatint, and etching. From 1905 onwards, he worked almost exclusively in Japanese-style wood engraving. In 1911, with Jules Chadel, he perfected this technique with the Japanese engraver Yoshijiro Urushibara.