What does it mean for a patent holder to commit to a standard-setting organization (SSO) to license its standard-essential patents (SEPs) on fair, reasonable, and nondiscriminatory (FRAND) terms? When is a royalty FRAND? Drawing from both legal theory and economic theory, I propose an interpretation of FRAND that distinguishes and reconciles the conflicting definitions of FRAND and provides courts a practical approach to identifying FRAND royalties. A proper understanding of a FRAND royalty requires recognizing the combinatorial value of standard-essential patents. That recognition reveals the fallacy in attempting to apply the “ex ante incremental value” rule to the determination of a FRAND royalty. FRAND royalties divide the aggregate royalties generated by the standard among the holders of patents essential to the standard. Such a division should maximize the surplus resulting from the standard’s creation. It must also satisfy an individual-rationality constraint for the patent holder and the licensee, thereby encouraging continued participation in the setting and implementation of open standards, as opposed to greater reliance on proprietary standards.