Analogy is a central component of language structure, language processing, and language change. This book addresses central questions about the form and acquisition of analogy in grammar. What patterns of structural similarity do speakers select as the basis for analogical extension? What types of items are particularly susceptible or resistant to analogical pressures? At what levels do analogical processes operate and how do processes interact? What formal mechanisms are appropriate for modeling analogy? What analogical processes are evident in language acquisition? Answers to these questions emerge from this book which is a synthesis of typological, experimental, computational, and developmental paradigms.