An organic light-emitting device includes: a first electrode; a second electrode; m emission units; and m−1 charge generation layer(s), each including an n-type charge generation layer and a p-type charge generation layer and being located between two emission units. The m emission units each include a hole transport region, an electron transport region, and an emission layer between the hole transport region and the electron transport region. An mth electron region included in an mth emission layer that is closest among the m emission units to the second electrode includes an mth electron transport layer. The mth electron transport layer is a single layer consisting of a first compound, the mth emission layer included in the mth emission unit includes a second compound, and the mth electron transport layer and the mth emission layer may be different from each other.