The presence and intensity of media influences television, radio, music, computers, films, videos, and the Internet are increasingly recognized as an important part of the social ecology of children and youth, and these influences have become more visible and volatile in recent decades. Research that explores the level and effects of media influences calls for measurements of the quantity and character of exposure to a variety of potentially overlapping media sources, an analysis of the content of the media output, and examination of the social context and relationships that are associated with the media experience. Recognizing the importance of this research, the Board on Children, Youth, and Families, under the auspices of the National Research Council and the Institute of Medicine, and with the sponsorship of the Henry J. Kaiser Family Foundation, held a workshop in March 2006. Its purpose was twofold: to examine the quality of the measures used in studies of the effects of media on children's health and development and to identify gaps in both research and practice. The goal was for a variety of experts to consider steps and strategies that could move this research forward and improve its utility for helping parents, practitioners, and policy makers guide young people in navigating a media-rich environment. Studying Media Effects on Children and Youth provides a summary of that discussion, supplemented with information from two papers prepared for the workshop. It begins with an examination of the potential impact of media exposure, followed by a description of the basic research questions and the methods currently used to study them. Methodological questions and challenges and theoretical approaches are described; they are discussed from the perspective of other kinds of epidemiological research. This report closes with a discussion of future directions for the field.