Golf balls comprising thermoplastic, thermoset, castable, or millable elastomer compositions are presently disclosed. These elastomer compositions comprise reaction products of polyisocyanates and telechelic polymers having isocyanate-reactive end-groups such as hydroxyl groups and/or amine groups. These elastomer compositions can be used in any one or more portions of the golf balls, such as inner center, core, inner core layer, intermediate core layer, outer core layer, intermediate layer, cover, inner cover layer, intermediate cover layer, and/or outer cover layer.