This guide covers pharmacy benefit law from the contract through the appeal. It begins with the two-contract architecture that creates the spread, then works provision by provision through the agreement terms that actually determine cost — the definitions of generic and rebate, the pricing model, the guarantee reconciliation methodology, and the audit clause. It covers the pharmacy side, including maximum allowable cost appeals, retrospective fees, and the procedural defenses that decide most audit disputes. It sets out the preemption line after the Supreme Court reopened state regulation, the fiduciary theory now aimed at plan sponsors, and the disclosure and attestation obligations Congress added. It then addresses the federal programs whose pricing definitions interact unpredictably, the appeal sequences in commercial, Part D, and Medicaid managed care, and closes with negotiation, governance, and litigation practice.