There is provided a novel polymer, a composition containing the polymer, and a novel adhesive composition containing the polymer from which a cured film having desired properties is obtained. A polymer comprising a structural unit of Formula (1): wherein Q is a bivalent group, R1 is a C1-10 alkylene group, a C2-10 alkenylene group or C2-10 alkynylene group, a C6-14 arylene group, a C4-10 cyclic alkylene group, etc., or a polymer comprising a structural unit of Formula (6): wherein Q4 is an allyl group, a vinyl group, an epoxy group, or a glycidyl group, and R5 is a bivalent organic group having a main chain containing only carbon atom or at least one of oxygen atom, nitrogen atom and sulfur atom in addition to carbon atom, a composition comprising the polymer, and an adhesive composition comprising the polymer and a solvent.