Attention‑Deficit Hyperactivity Disorder, Third Edition is a comprehensive, evidence‑based reference on ADHD that integrates contemporary research with practical clinical application. Written for clinicians, educators, and researchers, this edition provides a thorough overview of ADHD across the lifespan—covering etiology, neurobiology, diagnosis, assessment, and multimodal intervention strategies. It emphasizes current scientific advances and best practices in evaluation and treatment, making it a definitive resource for understanding ADHD in children, adolescents, and adults. Key Features: Up‑to‑date research: Reflects the latest findings in neurodevelopment, genetics, and neurocognitive models of ADHD. Comprehensive coverage: Examines ADHD from early childhood through adulthood, including gender and cultural considerations. Diagnosis and assessment: Detailed guidance on differential diagnosis, standardized testing, behavioral observations, and clinical interviewing. Multimodal interventions: Best‑practice treatment strategies, including behavioral therapy, pharmacotherapy, parent training, school‑based interventions, and combined approaches. Functional impairments: Discussion of academic, social, emotional, and occupational challenges associated with ADHD. Special topics: Coverage of co‑occurring conditions (e.g., learning disorders, anxiety, mood disorders), risk factors, and considerations for diverse populations. Practical tools: Case examples, clinical vignettes, tables, and decision‑making frameworks to support application in real‑world settings. Evidence‑based guidelines: Highlights current consensus and recommendations for assessment and intervention from major professional organizations.