The identification of varieties (dialects) — which requires relating linguistic features to major social categories such as class, age, gender, ethnicity and geographical origin — is one of the main achievements of variationist sociolinguistics. The task is central to the aims of sociolinguistics in two ways. First, it reveals the presence of structured heterogeneity within linguistic variation. Second, it accounts for the social meaning of linguistic variants: through the definition of bounded “social”, “regional” or “ethnic” varieties, so-called inter-speaker variation is directly associated with group membership and linguistic features become social identity markers.