Language Acquisition and Learnability is an accessible introduction to learnability theory and its interactions with linguistic theories. Working within the Principles and Parameters framework, the book surveys general concepts from formal learning theory and complexity theory, together with important findings from developmental psycholinguistics, historical linguistics and language processing. Written by a team of leading researchers it examines important techniques that can be used to obtain interesting and empirically testable predictions from parametric theories of language variation and includes chapters on syntax, diachronic syntax and the relationship between linguistic complexity and the form of parameters. Fully integrated, and complete with a large number of exercises to test readers on their understanding of the material, this book will become essential reading for students and researchers in linguistic theory.