An organic light-emitting device including: a first electrode; a second electrode facing the first electrode; an emission layer between the first electrode and the second electrode; and an electron transport region between the second electrode and the emission layer, wherein the emission layer includes a first host and a second host, the first host includes a first compound represented by Formula 1, the second host includes at least one selected from a second compound represented by Formula 2 and a third compound represented by Formula 3, and the hole transport region includes an amine-based compound represented by Formula 40: