This dissertation explores the role co-speech gesture plays as input in language learning, specifically with respect to the acquisition of anaphoric pronouns. Four studies investigate how both adults and children interpret ambiguous pronouns, and how the order-of-mention tendency develops in children. The results suggest that gesture is a useful cue for interpreting an ambiguous pronoun--adults and children 6-years and older appear to spontaneously utilize co-referential localizing gestures to inform their interpretation of a pronoun, and through training, 5-year-old children can also learn to do so. Moreover, 5-year-old children can utilize gesture to help them learn more about anaphora in general, not only picking up that the gesture maps onto the first mention name, but also forming the generalization that first-mentioned names in general are often the referent for pronouns, even in the absence of gesture. To a lesser degree, children can also make this generalization when the first-mentioned name is made salient in other ways without gesture, but training with gesture was particularly effective. Variation in the efficacy of training was related to individual differences in the ability to perceive gesture, implicit learning abilities, and to a lesser extent, verbal working memory abilities. The results suggest that co-speech gesture can indeed be thought of as a form of input for children acquiring language. Specifically, gesture is a useful source of information for developing an understanding of anaphoric pronouns, an aspect of language that is particularly challenging for English learning children to master. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]