This chapter presents a historical sketch of biolinguistics. It explains the knowledge of language, and explores how language develops in a child, and how language evolves in a species. These three questions are interrelated in a particular way. The question of how language develops in the child depends on understanding what the properties of the language system are, the answer to the question about what knowledge of language is. The third question about how language evolved in the species, depends crucially on the answers to the first two questions. In practice, one only has partial answers to all three questions, so that it becomes necessary to study all the questions in parallel, constantly revising the answers as new empirical data becomes available. A conceptual breakthrough was achieved with the development of the principles and parameters approach to language acquisition.