The study of sign languages contributes to our understanding of the human language faculty. Learning a sign language is in many ways like learning a spoken language, whether you learn it as a child as your first language or as an adult. There are however, important differences in this acquisition process and these shed light on the impact of modality on that process. The book project will study the differences (and similarities) between spoken and signed language acquisition. For example, learning to produce a sign requires the mastery of its different components: hand shape, location and movement. The hand shape turns out to be the most difficult aspect to master but analysis reveals that acquisition is influenced by both articulation complexity and the difficulty of perceptual discrimination, which is similar in many ways to spoken language acquisition.