This SAE Aerospace Information Report (AIR) provides a description of the interfacesand their requirements for generic and specific hydraulic actuation systems used in the flight control systems of manned aircraft. Included are the basic control system characteristics and functional requirements, and the essential interfaces (structural, mechanical, hydraulic power, control input, status monitoring, and environment). Major design issues, requirements, and other considerations are presented and discussed. The primary purpose of this document is to describe the interfaces to aid in the development of Interface Control Documents (ICDs) for primary flight control servoactuation systems in future applications. Due to the variety of applications, the number of, and type of, ICDs required for a particular application is left up to the user of this document. The lessons learned from previously developed production aircraft are discussed.