This study addresses the social and linguistic constraints on relativizer omission in restrictive relative clauses in a mainstream urban variety of Canadian English. Drawing on the framework of variationist sociolinguistics, the authors test an array of factors that have been traditionally implicated in the choice of relative marker (e.g., syntactic function of the relative marker; animacy and definiteness of the antecedent head NP; length of the relative clause), in addition to investigating less widely researched factors, such as the informational content of the matrix clause and the lexical specificity of the head NP. A variable rule analysis of nonsubject relative clauses extracted from 19 speakers stratified by age, sex, and education reveals that relativizer omission is socially sensitive and that properties of the matrix clause and adjacency effects are key determinants in the selection of the zero variant. Recurrent structural configurations exhibited by zero marked relative clauses in vernacular discourse are indicative of grammaticalization. Comparison with other varieties of English reveals that relativizer omission fails to pattern uniformly, suggesting that there is no vernacular norm in this area of the grammar. This absence of uniformity calls into question recent attempts by researchers to formulate a unitary account of relativizer omission by appealing to putatively general language processing constraints.