Spoken language systems allow users to interact with computers by spea
king to them. This paper focuses on the most advanced systems, which s
eek to allow as natural a style of interaction as possible. Specifical
ly this means the rise of continuous speech recognition - natural lang
uage understanding to interpret the utterance, and an intelligent dial
ogue manager which allows a flexible style of 'conversation' between c
omputer and user. This paper discusses the architecture of spoken lang
uage systems and the components of which they are made, and describes
both a variety of possible approaches and the particular design decisi
ons made in some systems developed at BT Laboratories. Three spoken la
nguage systems in the course of development are described - a multimod
al interface to the BT Business Catalogue, an e-mail secretory which c
an be consulted over the telephone network, and a multimodal system to
allow selection of films in the interactive TV environment.