This International Standard defines a CCSDS file delivery protocol (CFDP) and associated service for application in the space environment. It is intended for use over the current and envisaged packet delivery services used in the space environment, including ⎯ CCSDS conventional packet telecommand; ⎯ CCSDS conventional packet telemetry; ⎯ CCSDS advanced orbiting systems (AOS) path service. It may also operate over a wide variety of ground network services, including those specified by the CCSDS for cross-support purposes. The protocol operates in the space-to-ground, ground-to-space, and space-tospace directions of transfer. It may be initiated by the file sending or receiving entity. In the interests of interoperability, protocol elements are included for generalized forms of standard file manipulation operations based on assumptions of a common model for a ‘filestore’, or medium used to store files. It is recognized, however, that the precise nature and capabilities of filestore management systems are operating-system dependent and, for that reason, the protocol assumes a virtual filestore and associated services that an implementation must map to the capabilities of the actual filestore used. The scope and field of application are furthermore detailed in subclauses 1.2 and 1.3 of the enclosed CCSDS publication.