This software engineering Standard concerns the "product software", i.e. software that is part of a space system product tree and developed as part of a space project. This Standard is applicable, to the extent defined by the tailoring process, to all the elements of a space system, including the space segment, the launch service segment and the ground segment. This Standard covers all aspects of space software engineering including requirements definition, design, production, verification and validation, transfer, operations and maintenance. It defines the scope of the space software engineering processes and its interfaces with management and product assurance, which are addressed in the Management (-M) and Product assurance (-Q) branches of the ECSS System, and explains how they apply in the software engineering processes. This Standard reflects the specific methods used in space system developments, and the requirements for the software engineering processes in this context. Together with the requirements found in the other branches of the ECSS Standards, this Standard provides a coherent and complete framework for software engineering in a space project. This Standard is intended to help the customers to formulate their requirements and suppliers to prepare their responses and to implement the work. This Standard is not intended to replace textbook material on computer science or technology, and such material is avoided in this Standard. The readers and users of this Standard are assumed to possess general knowledge of computer science. The scope of this Standard is the software developed as part of a space project, i.e. "Space system product software". This Standard also applies to the development of non-deliverable software that affects the quality of the deliverable product. This Standard may be tailored for the specific characteristics and constraints of a space project in conformance with ECSS-S-ST-00.