How do adults learn new languages? Why do some people learn new languages easily, while others struggle? What can language teachers do to make the learning experience as successful as possible? The course addresses these and related questions by providing a critical introduction to recent theories of instructed second language acquisition (ISLA). We will reflect on these issues through readings and discussion, and we will engage them on a practical level through one-on-one ESL tutorials with participants from the greater Princeton community, in collaboration with ProCES.