Referential expressions (REs) have been investigated in L2 English but to date there is no single study that systematically and simultaneously analyzes the development and acquisition of the multiple factors that constrain the choice of REs in natural discourse production. We investigate L1 Spanish-L2 English learners across three proficiency levels versus an English control group from the COREFL corpus. An analysis of both the RE and its antecedent(s) reveals that different intra- and extralinguistic factors constrain the choice of REs (information status, activated antecedents, syntactic configurations, characterhood, within-task effect, and proficiency level). L2 learners (L2ers) are sensitive to some factors but are unable to fully attain native-like levels even at advanced stages. They do not transfer null subjects from their L1 contrary to previous L2 research, and do not find all contexts at the syntax-discourse interface equally problematic, thus confirming previous theoretical proposals and empirical findings.