This book provides students and researchers interested in language acquisition with comprehensible and practical information on the most frequently used methods in language acquisition research. It includes contributions on first and child/adult second language learners, language-impaired children, and on the acquisition of both spoken and signed language. Part I discusses specific experimental methods, explaining the rationale behind each one, and providing an overview of potential participants, the procedure and data-analysis, as well as advantages and disadvantages and dos and don’ts. Part II focuses on comparisons across groups, addressing the theoretical, applied and methodological issues involved in such comparative work.