Pharmacy benefit managers (PBM) are important intermediaries in the pharmaceutical supply chain in the US. Under the general umbrella of administering outpatient prescription drug benefits for health plans, PBMs took on a variety of roles, including managing the drug formulary, negotiating with drug manufacturers and retailers, and processing drug claims. PBMs have come under scrutiny as we have learned more about the scale of prescription drug rebates and other payments between manufacturers and intermediaries in the prescription drug market. A lingering question is the underlying value of PBMs for payers and for patients.