This book traces a single developmental dimension, joint attention—the capacity to coordinate looking, pointing, and shared focus with another person—through its role in the diagnosis, neuroscience, genetics, and treatment of autism spectrum disorder (ASD). Most clinicians and researchers encounter this material in pieces. A graduate student can master one slice of autism science—early intervention outcomes, say—without ever seeing how it connects to diagnostic criteria or the underlying neurobiology. Peter C. Mundy, the researcher who first identified joint attention as a core symptom dimension of autism, wrote this book to close that gap. He examines what joint attention is, when it emerges in the first months of life, how it is measured in diagnosis, what neuroimaging and genetic research reveal about its biological basis, and what decades of randomized controlled trials show about interventions that target it. The volume builds a single, evidence-based case for why joint attention deserves a more central place in how we understand ASD.