Synthesizing an explosion of recent research, this book presents dramatic advances in understanding and treating autism spectrum disorder (ASD) in very young children. Leading authorities describe the innovative tools and methods that are enabling clinicians to more effectively identify 0- to 5-year-olds with the disorder and those at risk for related problems. Chapters discuss the early core symptoms and co-occurring characteristics of ASD, the best diagnostic instruments, and lessons learned from large-scale screening and surveillance, including sibling studies. The book reviews evidence-based interventions and explores practical issues in treatment of young children and their families.