The purpose of this paper is to provide an overview of second language acquisition (SLA) research over the past several decades, and to highlight the ways in which it has retained its original applied and linguistic interests, and enhanced them by addressing questions about acquisition processes. As the paper will illustrate, SLA research has become increasingly bi-directional and multi-faceted in its applications. These many applications to and from the study of SLA reflect the robustness and vitality of the field.