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. 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.