The What Works Briefs are a series of short, easy-to-read, "how-to" information packets designed to: (1) promote practices that support young children's social and emotional development and prevent challenging behaviors; (2) highlight practices, strategies, and intervention procedures that have been found to effectively prevent and address children's challenging behaviors; (3) offer a variety of evidence-based practices, strategies, and intervention procedures; (4) present clear scientific and value-based support for the practices' effectiveness; (5) help early childhood professionals and families of young children select practices, strategies, and intervention procedures; and (6) offer procedures that have been used in various settings, such as homes, classrooms, centers, and other community environments with a variety of children, families and professionals. This introduction to the briefs describes what each brief contains, how the briefs can be used, who can benefit from the briefs, and five guiding principles of sound teaching that need to be in place to produce meaningful change for children and families. The scope of the briefs is limited to prevention and intervention practices in the social-emotional domain for children ages 2 through 5. The briefs also include policies and procedural and administrative practices needed to support the use of evidence-based practices. (SG)