In this chapter, the authors focus on linguistic variation, by which they mean the ways in which individuals or groups construct and use diverse forms for expressing the same meanings. They discuss variation from the perspective of sociolinguistics to demonstrate that some of the differences observed within groups of bilingual speakers. The authors provide an overview of how variation has been conceptualized and accounted for in the scholarly literature on bilingualism. They also discuss how bilingual and contact communities have been studied traditionally, drawing parallels between the notions of restricted speakers and language shift in the sociolinguistic and language contact literature and proficiency and language dominance in psychology. The authors show that these fields, though disparate in their goals, have been similarly engaged in accounting for the variation observed, particularly within bilingual communities, as a function of proficiency and dominance.