Health plans and hospitals have long used drug formularies, but the processes by which formulary committees made decisions have typically lacked transparency and scientific rigor. A growing number of organizations have begun implementing formulary guidelines issued by the Academy of Managed Care Pharmacy (AMCP). These guidelines call for health plans to request formally that drug companies present a standardized "dossier" that contains detailed information not only on the drug's effectiveness and safety but also on its economic value relative to alternative therapies. This paper describes the guidelines, reviews progress to date, and analyzes several critical issues for the future.