A polymer and an organic light-emitting device including the polymer. An example of the polymer is wherein in Formula 1, Ar1 is each independently represented by -(Q1)n-, and Q1 is selected from the group consisting of a substituted or unsubstituted C5-C30 arylene group, a substituted or unsubstituted C4-C30 heteroarylene group, a substituted or unsubstituted C2-C30 alkenylene group, and a group represented by —N(Z1)—, and n is an integer from 1 to 10, and n groups of Q1 in -(Q1)n- is identical to or different from each other, and X1 and X2 are each independently selected from the group consisting of —O—, —S—, —N(Z2)—, and —C(Z3)(Z4)—.