This textbook surveys the current knowledge on substance use disorders (SUD), summarizing scientific evidence from numerous fields. It uses a biopsychosocial framework to integrate the many factors that contribute to addictions, from genetic predispositions, neurological responses caused by drugs, co-occurring psychiatric disorders, personality traits, and developmental conditions to cultural influences. Real-life vignettes and first-person accounts build understanding of the lived experience of addiction. The currently accepted practices for diagnosis and treatment are presented, including the role of 12-step programmes and other mutual-assistance groups. The text also investigates the research methods that form the foundation of evidence-based knowledge. The main body text is augmented by study guideposts such as learning objectives, review exercises, highlighted key terms, and chapter summaries, which enable more efficient comprehension and retention of the book's material.