This collection brings together Naoki Fukui's pioneering body of work on Merge from the perspectives of theoretical syntax and neuroscience. Part I presents an overview of the development of the theory of Merge and its current formulations in linguistic theory, while Part II focuses on experimental research on Merge in the brain science of language, demonstrating how new techniques and the results they produce can inform the study of syntactic structure in the future. This book presents an innovative unified account of the study of Merge and paves new directions for future research for students and scholars in theoretical linguistics, neuroscience, syntax, and cognitive science.