Human communication combines language with gesture. Gesture contributes to the uniquely human ability to communicate about an infinite number of ideas in an efficient way and to generate representations that are useful for thinking. Gesture and language can be distinguished by distinct underlying modes of thinking and by gradations of conventionalization and the transparency of form-meaning relations. However, it is not always possible or useful to draw a sharp line between gesture and language. In this Review, we first describe how speakers and signers produce facial, manual, and body gestures. Then, we describe how representational gesture encodes information, considering the constraints from properties of languages, and how speakers and signers orchestrate language and gesture. Next, we review how gesture production shapes thinking for both signers and speakers, and consider gesture comprehension and how the meaning of gestures is integrated with language. We conclude with suggestions for further exploration of gesture as a critical expression of the human mind.