An organic light-emitting device (OLED) includes a first electrode; a second electrode facing the first electrode; an emission layer (EML) between the first electrode and the second electrode; a hole transport region between the first electrode and the EML; an electron transport region between the EML and the second electrode; and an interlayer between the EML and the hole transport region, wherein the interlayer includes an amine-based compound represented by Formula 1 or 2: where Ar1, Ar2, R1-R4, Z11-Z21, p, and q are as defined in the specification.