An organic light-emitting device includes a substrate, an anode on the substrate, a hole transport region on the anode, an emission layer on the hole transport region, an electron transport region on the emission layer, and a cathode on the electron transport region, wherein the electron transport region includes an electron injection layer including a first material including at least one of a halide of an alkali metal, and a second material including at least one of a lanthanide metal and a alkaline earth metal, and wherein the cathode contacts the electron injection layer and includes a first metal including at least one of silver, gold, platinum, copper, manganese, titanium, cobalt, nickel, and tungsten, and a second metal including at least one of a lanthanide metal and an alkaline earth metal, wherein an amount of the first metal is equal to or greater than that of the second metal.