This chapter describes what happens to the manual modality under two distinct circumstances: (1) when it accompanies speech, and thus forms part of language; and (2) when it is used instead of speech as the primary modality for communication, and thus is itself language. It turns to the form co-speech gesture assumes and then explores its communicative and cognitive functions. Co-speech gesture is thus not structured like a conventional linguistic system. It has its own representational properties, which work together with speech to form an integrated system. The information gesture conveys can be quite different from the information conveyed in the speech it accompanies. The chapter describes the hand movements people produce in the absence of speech, deals with conventional sign languages created by deaf communities. Sign languages of the deaf are autonomous languages, independent of the spoken languages of hearing cultures.