The Extra Stage Cube (ESC) interconnection network, a fault-tolerant structure, is proposed for use in large-scale parallel and distributed supercomputer systems. It has all of the interconnecting capabilities of the multistage cube-type networks that have been proposed for many supersystems. The ESC is derived from the Generalized Cube network by the addition of one stage of interchange boxes and a bypass capability for two stages. It is shown that the ESC provides fault tolerance for any single failure. Further, the network can be controlled even when it has a failure, using a simple modification of a routing tag scheme proposed for the Generalized Cube. Both one-to-one and broadcast connections under routing tag control are performable by the faulted ESC. The ability of the ESC to operate with multiple faults is examined. The ways in which the ESC can be partitioned and permute data are described. Copyright © 1982 by The Institute of Electrical and Electronics Engineers, Inc.