This chapter deals with variation in second language acquisition (SLA), specifically variationist sociolinguistic research approaches, which share a common interest in variability, systematicity in variability, form function relations, language variation and change. The chapter outlines the contributions of variation theory and methodology to SLA research. It describes variation theory, early variationist work on SLA, concepts and models and recent developments. Recent work, instead of focusing on English L2, takes into account a wide range of languages, permitting more universalistic conclusions. It deals with a wider range of speaker populations such as heritage and migrant speakers. Network analysis techniques provide more detail on social context. A move away from essentialist criteria, towards “third wave” variationist L1 research gives a more ethnographic emphasis to L2 variationist studies. Work on language attitudes and L2 involves perception studies, studies of lexical frequency or geographic variety. Variationist L2 research contributes to our understanding of some central themes and topics in SLA research. It avoids prescriptivism and norms, avoids seeing the L2 speaker as a deficient L1 speaker and instead examines language use within its own terms.