Evolving techniques and the opening market have contributed to new aspects which have made a revision of the brochure issued in 1992 (Ref. 69). The purpose of this document is to provide a simple guide for designing an outdoor AC substation, considering the systems requirements, the most suitable site, and design of the equipment to be installed. It provides advice on the general principles, relevant IEC standards and CIGRE reports, as appropriate, and also takes the economic factors involved.