This course examines language acquisition by different populations: first language acquisition by normal, deaf and impaired children; first language re-acquisition by aphasic patients; second language acquisition by children and adults. The question that we will ask is the following: what are the similarities and differences across acquisition contexts? Comparative theoretical approaches will be examined in order to gain an insight into the following topics: evidence for innate linguistic endowment, the stages in the development of grammar, the role of input. An important component will be the analysis of both spontaneous corpora and experimental work.