This book explores the socially and individually determined nature of media literacy, addressing the central question of how individuals' media activity can be explained and evaluated. It examines people's media activity through the relationship between their competence to act and actual actions. Further, the book discusses the social factors that foster self-determined media activity, including people's abilities and skills and the associated knowledge that facilitates such skills, from the perspectives of various social science disciplines. Lastly, it applies these theoretical reflections to two empirical studies. Overall, this book provides a fundamental introduction to theories of media socialization, media literacy and media competence, and to the relation between media and socialization. It analyses international discourses on children, media, media literacy, and digital literacy. This book is of interest to scholars and researchers in the field of media studies, including media sociology and media education, communication, and cultural studies.