The study of second language acquisition (SLA) forms a young academic discipline, emerging from fundamental paradigm shifts in SLA’s parent disciplines, linguistics and psychology. This paper gives a brief overview of how the study of SLA came into existence, formulates the fundamental questions concerning SLA, reviews some recent developments, and identifies possibilities and challenges for SLA theory construction and empirical research in the near future. To tackle the fundamental issues of SLA successfully, it is mandatory that SLA researchers, of whom the majority currently has a linguistic background, collaborate with researchers in psychology and other disciplines.