Looking back at the past 15 years in the field of second language acquisition (SLA), the authors select and discuss several important developments. One is the impact of various sociocultural perspectives such as Vygotskian sociocultural theory, language socialization, learning as changing participation in situated practices, Bakhtin and the dialogic perspective, and critical theory. Related to the arrival of these perspectives, the SLA field has also witnessed debates concerning understandings of learning and the construction of theory. The debate discussed in this article involves conflicting ontologies. We argue that the traditional positivist paradigm is no longer the only prominent paradigm in the field: Relativism has become an alternative paradigm. Tensions, debates, and a growing diversity of theories are healthy and stimulating for a field like SLA.