The paper describes the electrical installation in the Royal Festival Hall and illustrates some of the problems encountered in its design.Lightning protection, the power installations, and the primary, secondary and stage lighting are described, special attention being given to the development of the dimming arrangements for coldcathode lighting.The description of the sound amplification system includes arrangements for hearing-aids, simultaneous interpretation, and an unorthodox type of interval signal.Other features of the installation are the provisions made for B.B.C. sound and television broadcasts, stage signalling, cueing systems and internal telephones.