Consolidation among hospitals and physician practices is driving a steady rise in health care costs. Employers who purchase insurance and the payers that negotiate on their behalf have a limited set of tools available to counter providers’ demands, but they have also displayed a complacency that has allowed prices to rise with little resistance. In a post for the Health Affairs blog, Sabrina Corlette, Jack Hoadley, and Katie Keith share findings from a series of market-level case studies on responses to provider consolidation.