The goal of the proposed research is to understand the nature and function of the mappings between words and concepts in memory. The proposed studies specifically address the experience of the novice adult bilingual. We argue that because these adults already have a rich set of interconnections in memory between words and concepts for their first language, the process of acquiring a second language may reveal the workings of these memory systems in a clearer way than studies of first language acquisition in which the acquisition of concepts and words are necessarily correlated. Towards this goal, we first describe a set of preliminary experiments which reveal a shift from lexical to coceptual processing of the second language with increasing expertise. Two sets of experiments then address this conceptual shift in second language learners by comparing novice and more expert bilingulas in naming translation and priming tasks, the first set of experiments examines the differences between the representations and processes characteristic of more and less fluent bilingulas. The second set of experiments is concerned with those factors that mediate the observed conceptual shift. Three different possibilities are considered that alone or in combination are expected to influence a shift towards conceptual processing of the second language increasing vocabulary size in the second language acquisition of syntax and sentence-level processes in the second language and ability to inhibit the automaticity associated with the first language. The results of these experiments will have important implications for theories of lexical and conceptual memory for models of the acquisition of new skills in adulthood and for second language instruction.