This article provides an overview of the history of research on adolescence. In our view, the history of the scientific study of adolescence has had two overlapping phases and is now on the cusp of a third. The first phase, which began early in the 20th century and lasted about 70 years, was characterized by grand theoretical models that purportedly pertained to all facets of adolescent development. The major studies of adolescence during this period were a theoretical, descriptive accounts. The second phase, which began in the mid-1970s and continues today, has been characterized by more focused hypothesis testing, an interest in developmental plasticity and in diversity, and in the application of science to real-world problems. We are now seeing the emergence of a third phase, in which the field of adolescent development is serving as an exemplar of the sort of developmental science that can be used by policy makers and by practitioners to advance civil society and to promote positive development.