This Element provides an overview of research considering variables deemed to impact bilingual language acquisition, and highlights research outcomes from a variety of disciplines. An exploratory study takes into account these variables and examines the language acquisition of adult Spanish-English bilinguals across a range of domains in their two languages. The results demonstrate that the highly interactive nature of bilingual speakers' languages is in line with a holistic view of the dynamic, interdependent nature of bilingualism as described by usage-based theories and dynamic systems theories, and by the conceptualization of bilingual language from a Dynamic Interactive Processing Perspective.