Interviews with a purposive sample of 32 early adopters of advanced primary care and/or accountable care organization (ACO) models revealed that primary care physicians perceive many potential benefits of joining an ACO, including care coordination staff, data analytics, and improved communication with other providers. However, physicians were also concerned about added “bureaucratic” requirements, referral restrictions, and a potential inability to recoup investments in practice improvements. Both the advantages and disadvantages of joining an ACO seemed exacerbated for small practices, since they are most likely to benefit from additional resources yet are most likely to chafe under added bureaucratic requirements.