This study addresses the debate about whether adult language learners have access to the principles and parameters of universal grammar in constructing the grammar of a second language. The data are based on two related experiments. The first examines the interpretation of English reflexive pronouns by native speakers of Japanese and of Spanish. The second experiment examines the interpretation of the Japanese reflexive zibun by native speakers of English and of Chinese. Three hypotheses are evaluated: (a) that UG is unavailable, and that processing strategies or other non-linguistic principles guide second language acquisition; (b) that UG is available only in the form in which it is instantiated in the learner's native language; (c) that UG is fully available, including the ability to re-set parameters to UG-sanctioned values not instantiated in the learner's native language. The results show that learners observe constraints defined by Manzini and Wexler's parameterized version of Principle A of the binding theory and support the proposal that adult learners have access to universal grammar. A final chapter reviews the experimental data in the light of recent accounts of cross-linguistic variation in the grammar of anaphors which reject parameterization of the binding principles in favor of a movement to INFL analysis.