Significant differences in language and self-regulation skills exist among children when they enter formal schooling. Contributing to these language differences is a growing population of dual language learners (DLLs) in the United States. Given evidence linking self-regulatory processes and language development, this study explored bidirectional associations between English expressive vocabulary and self-regulation skills for monolingual English and DLL preschool children (N = 250) from mixed-income families in Los Angeles. Across three time points, findings provide initial support for bidirectionality between these developing skills for both monolinguals and DLLs. Results provide strong empirical support for vocabulary serving as a leading indicator of self-regulation skills in preschool. Findings also suggest that early self-regulation skills play a particularly important role for vocabulary development.