An organic light-emitting device includes: a first electrode; a second electrode; an organic layer between the first electrode and the second electrode and including an emission layer; and at least one organometallic compound of the present embodiments. In the organic light-emitting device, the emission layer may further include a host, and the at least one organometallic compound may be a phosphorescent material or a delayed fluorescent material. The organic light-emitting device including the organometallic compound may have a low driving voltage, a high luminance, a high efficiency, and a long lifespan.