An organic light-emitting device includes a first electrode; a second electrode facing the first electrode; an emission layer between the first electrode and the second electrode; and a hole transport region between the first electrode and the emission layer, wherein the hole transport region includes a hole transport layer, and a hole auxiliary layer between the hole transport layer and the emission layer. The hole auxiliary layer includes a first compound represented by Formula 1, and the hole transport layer includes a second compound represented by Formula 2: