Medicare funds health-care services for 60 million elderly and disabled Americans. Of these, 39 million receive coverage through a plan known as “Traditional Medicare” or “Medicare Fee-for-Service” (MFFS) that the federal government administers directly. Increasing numbers of seniors—21 million in 2019—enroll in Medicare Advantage (MA), choosing from competing plans managed by private insurers. MA provides an incentive for plans to develop innovative care arrangements, but the rules under which MA plans operate can be restructured so that more of the efficiency gains can be passed on to beneficiaries.