With the recent introduction of extra high voltage transmission on the order of 500 kv to 750 kv, the electrical power industry is experiencing a tremendous physical change. It is now possible to bring energy from power sources thousands of miles from a load center. This challenge of ingenuity has kindled an interest in these huge transmission projects and has focused attention on engineering design that goes into transmission lines in general. This paper deals with the knowledge and experience that form the basis for the design methods developed and used by the Southern California Edison Company for transmission tower foundations. Particular attention is given to the concrete belled cylindrical pile which, because of its economic advantage over other footing types, makes up the bulk of the tower foundations now being constructed. Also treated are several areas of design and construction for which a better understanding of the soil-structure interaction appears to offer some potential for the development of more economical tower foundation designs.