During the past ten years, research on second language acquisition (SLA) has expanded; at the same time, different models and hypotheses have been proposed to explain and account for the processes underlying SLA. Four models seem to be dominant at the present time: (1) the monitor model, which distinguishes between implicit or unconscious language acquisition and explicit language learning; (2) the discourse approach which emphasizes the relationship between the form and function of linguistic structures; (3) the neurofunctional perspective, which looks at SLA processes through two interrelated systems, macro-behavioral and neurofunctional, and which distinguishes between primary, secondary, and foreign language learning; and (4) the acculturation model, based on social and psychological factors, which claims that acculturation is the major cause of second language acquisition. Each model is reviewed, evaluated, and critiqued from an experimental perspective. It is argued that the acculturation model may establish the starting point from which experimental research on SLA might be pursued. (Author/AMH)