An organic light-emitting device includes: a first electrode; a second electrode facing the first electrode; and an organic layer located between the first electrode and the second electrode and including an emission layer, wherein the emission layer includes a host and a dopant, the host includes a first compound and a second compound, and the first compound, the second compound, and the dopant are different from one another. Two compounds in the host included in the emission layer may have different HOMO and LUMO energy levels and may form an exciplex, and a difference between a HOMO energy level and a LUMO energy level of the exciplex (ΔEexciplex) may be greater than a difference between a HOMO energy level and a LUMO energy level of the dopant (ΔEdopant).