RecruitingBehavioural interventionActivating SilverSneakers Benefits for Seniors With OsteoarthritisThe aim of this pragmatic randomized controlled trial is to test the effects of a brief proactive care intervention involving mailed material and two phone calls on: (1) increasing participation in SilverSneakers exercise programs among older adults with osteoarthritis; (2) improving physical, social and psychological outcomes identified as important to older adults with osteoarthritis; and (3) reducing costly osteoarthritis-related health service use. Approximately 1,454 older adults with osteoarthritis who have SilverSneakers access through their Medicare Advantage plan, but no prior SilverSneakers use, will be recruited to participate across the United States. Key outcome measures will be assessed over a two-year follow-up period.