An organic light-emitting device is provided. The organic light-emitting device includes: a first electrode; a second electrode; and an organic layer between the first electrode and the second electrode and including an emission layer, the organic layer including a first compound, a second compound, and a third compound. The first compound, the second compound, and the third compound are each independently an azine-based compound represented by one selected from Formulae 1-1 to 1-5, except for a case where the first compound, the second compound, and the third compound concurrently include an azine-based compound represented by Formula 1-3.