The majority of children acquire language effortlessly but approximately 10% of all children find it difficult especially in the early or preschool years with consequences for many aspects of their subsequent development and experience: literacy, social skills, educational qualifications, mental health and employment. With contributions from an international team of researchers, this book is the first to draw together a series of new analyses of data related to children’s language development, primarily from large-scale nationally representative population studies, and to bring a public health perspective to the field. The book begins with a section on factors influencing the patterns of language development. A second section explores continuity and change in language development over time. The third explores the impact on individuals with developmental language disorders (DLD), the effectiveness of available interventions, and broader issues about the need for equity in the delivery of services to those with DLD.