This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book examines the relationship between assessment systems and efforts to advance equity in education at a time of growing inequalities. It considers the political motives behind the expansion of an assessment industry and a growth in consequential accountability systems. The book examines in detail the complex historical intersections of assessment and educational equity with particular attention to the implications for marginalized populations of students and their families. It explores the assessment and identification practices that seek to classify different categories of learners, including children with Limited English Proficiency, with special needs and disabilities and with behavioural problems. The book examines the production of inequalities within assessment in relation to race, class, gender, and disability and the overrepresentation of particular groups of children, including certain cultural minorities in special education and children living in poverty among those diagnosed with mental disorder.