This paper discusses in broad terms the design of a radically new family of multiplex terminals, designated the L multiplex, designed to work with any of several broadband transmission facilities. The relevant historical background of multiplex terminals is covered and design objectives for the new equipment are outlined. The new multiplex takes advantage of advances in the state of the art to reduce the size of equipment and increase reliability, while it retains the proven advantages of older equipment. Other advantages of the new multiplex include in-service maintenance, decentralized carrier supplies, and increased flexibility. The latter permits its use with as few as 60 or as many as 1860 voice channels and also adapts it for use with wideband data service. Compatibility with older multiplex equipment was maintained where possible, but in order to meet future demands for broadband service, it was decided to modify older equipment rather than compromise the design of the new to maintain compatibility.