Book excerpt: When we speak, we often spontaneously produce gestures. Such gestures are an integral part of face-to-face verbal communication. The relationship between speech and gesture is the theme of this Special Issue. The articles cover a wide range of issues: cultural differences, language and gesture development, cognitive development, bilingualism, foreign language learning, persuasion, and "common grounds" between the speaker and the addressee. The Special Issue is of interest not only to those who study the multimodal nature of communication, but also to those who seek new insights into psycholinguistic issues, using gesture as the "window" into the speaker's mind.