Purpose: This paper reports a case study of 7 Critical Access Hospitals' (CAH) and 1 rural referral hospital's successful collaboration to develop a shared formulary. Methods: Study methods included document reviews, interviews with key informants, and use of descriptive statistics. Findings: Through a systematic review and decision process, CAH formularies ranging in size from 667 to 1,351 items were compared, rationalized, and consolidated resulting in an 803-item shared formulary. While the individual CAHs were generally expected to list and stock the same 803 items in the shared formulary's pharmacy information system, they could individually determine the amount to be stocked for each item, as well as stock additional items not included on the shared formulary to reflect local provider preferences and services provided. Final stocked formulary items ranged from 592 to 786 items among the 7 CAHs. Major challenges and lessons learned in the course of developing a shared formulary related to: Meeting Logistics, Facilitator to Manage the Process, Organizing the Review Process, Management Support, Stakeholder Participation, Working Collaboratively, Decision-Making Process, Clarity of Charge, Meeting the Needs of Unique Services, Communicating with Providers, and Adjusting to a Shared Formulary. Conclusions: Collaborating in the development of a shared formulary allows for a greater range of decision-making expertise, shared workload, and an improved formulary. An organized and well-managed group decision-making process is essential to a successful collaboration.