2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/173809The aim of this article is to give a criterion, generalizing the criterion introduced by Priddy for algebras, to verify that an operad is Koszul. We define the notion of a Poincare-Birkhoff-Witt basis in the context of operads. Then we show that an operad having a Poincare-Birkhoff-Witt basis is Koszul. Besides, we obtain that the Koszul dual operad has also a Poincare-Birkhoff-Witt basis. We check that the classical examples of Koszul operads (commutative, associative, Lie) have a Poincare-Birkhoff-Witt basis.24 pages, in english. Changes in v3 : Correction concerning the graded case and some other minor correctionsAlgebraic Topology18D50 (55D48); 16S37text