An organic light-emitting device includes a first electrode; a second electrode facing the first electrode; and an organic layer between the first electrode and the second electrode, the organic layer including an emission layer. The emission layer includes at least one heterocyclic compound of Formula 1. The heterocyclic compound may be a host or a delayed fluorescent dopant. The organic light-emitting device including the heterocyclic compound may have a low driving voltage, high efficiency, high luminance, and a long lifespan.