Pierre-Étienne Piestre, known as Eugène Cormon (5 May 1810 – March 1903), was a French dramatist and librettist. He used his mother's name, Cormon, during his career.

Cormon wrote dramas, comedies and, from the 1840s, libretti; around 150 of his works were published. He was stage manager at the Paris Opéra from 1859 to 1870, and administrator of the Théâtre du Vaudeville from 1874.

His libretti include Les dragons de Villars (with Lockroy), Gastibelza (with d'Ennery) and Les pêcheurs de Catane (with Carré) for Maillart, Les pêcheurs de perles (with Carré) for Bizet, Robinson Crusoé (with Crémieux) for Offenbach, and Les Bleuets (with Trianon) for Cohen.

The Fontainebleau act as well as the auto-da-fé scene of Verdi's opera Don Carlos is based in part on Cormon's 1846 play Philippe II, Roi d'Espagne ("Philip II, King of Spain").

At the Moscow Art Theatre in 1927 the seminal Russian theatre practitioner Constantin Stanislavski staged Cormon's melodrama The Gérard Sisters (The Two Orphans), which he co-wrote with Adolphe d'Ennery.