This article discusses provider agreements that can be accessed by various different payers rather than solely by the single parties that originated the agreements. In recent years, these "multipayer agreements" have been used both more widely and for wider purposes than in the past. The application of multipayer agreements is becoming more complex and fraught with errors, which often disadvantage imaging practices. Even without error, the broader use of multipayer agreements can have a significant and often unrecognized adverse impact on reimbursement for imaging services. This article describes multipayer agreements in detail, including why they were originally developed, why payers use multipayer agreements, and why their use has expanded recently, notably to national insurers. Furthermore, this description identifies two types of multipayer agreements. A "keychain" agreement allows multipayer plans to unilaterally add new payers to existing provider agreements, each of which becomes entitled to the discounts and other benefits conferred by the base agreement. A "power-of-attorney" agreement allows multipayer plans to effectively bind providers to new provider agreements unilaterally. Three examples of issues confronted by imaging practices in the course of administering existing multipayer agreements are described in some detail. Last, the article provides several suggestions for evaluating and containing an imaging practice's potential exposure to multipayer agreements.