This investigation incorporates insights from sociolinguistics and second language acquisition into the study of variable subject expression in second-language (L2) Spanish. The data come from sociolinguistic interviews completed by graduate-level non-native speakers (NNSs) and native-speakers (NSs) of Spanish. In order to more fully describe the L2 system, the dependent variable of subject expression is expanded from a binary variable (null vs. overt) to an examination of the full range of subject expression forms produced with finite verbs. The relationship between the subject expression forms used by the NNSs and two independent linguistic variables, person and number of the verb and specificity of the referent, are analyzed statistically and qualitatively. The L2 data are also compared to the NS sample. The results show that both participant groups produce six different subject expression forms: lexical noun phrases, null subject pronouns, overt subject pronouns and indefinite, interrogative and demonstrative pronouns, but that the frequency with which they use these forms differs significantly between groups. The frequency of occurrence of subject expression forms also differs significantly across the categories of each independent linguistic variable for both the NNSs and the NSs, and there are qualitative similarities and differences between the two groups. The findings demonstrate that a binary dependent variable does not exist for subject expression in Spanish and that examining independent variables individually provides a detailed understanding of how subject expression use varies across groups and across linguistic contexts.