Chapter 9 provides methods for uncovering the mechanisms by which children learn language. First language acquisition is an important sub-discipline of linguistics because it offers a unique window into the nature of the human faculty for language. Currently only around 2 per cent of the world’s 6,000–7,000 languages have acquisition studies, and most of these are of major European languages. More field studies of a diverse range of languages are needed to be able to answer questions about acquisition and the mind. This chapter gives students the tools to design field studies of acquisition, including methods for creating longitudinal corpora of individual children and cross-sectional experimental studies of a cohort of children. Importantly, we discuss techniques for overcoming some of the difficulties presented by field studies of acquisition, for example recruitment of children and their families, transcription of child speech where teams of native-speaker transcribers are not available, and specific ethical considerations associated with children.