An organic light-emitting device and an organometallic compound are provided, the organic light-emitting device including a first electrode; a second electrode; and an organic layer between the first electrode and the second electrode and including an emission layer, wherein the organic light-emitting device further includes an organometallic compound represented by Formula 1: wherein, M, Y1 to Y4, T1 to T4, A1 to A5, X1, X2, L1 to L3, a1 to a3, R1 to R5 and b1 to b5 are the same as defined in the specification.