A categorization paradigm was used to investigate the relations between lexical and conceptual connections in bilingual memory. Fifty-one more fluent and less fluent English-French bilinguals viewed category names (e.g., vegetable) and then decided whether a target word (e.g., peas) was a member of that category. The category names and target words appeared in both English and French across experimental conditions. Because category matching requires access to conceptual memory, only relatively fluent bilinguals, who are able to directly access meaning for their second language, were expected to be able to use category information across languages. The performance of less-fluent bilinguals was expected to reflect reliance on lexical-level connections between languages, requiring translation of second-language words. The results provided evidence for concept mediation by more-fluent bilinguals, because categorization latencies were independent of the language of the category name. However, the performance of less-fluent bilinguals indicated that they did not follow a simple lexical translation strategy. Instead, these subjects were faster at categorizing words in both languages when the language of the category name matched the language of the target word, suggesting that they were able to access limited conceptual information from the second language. A model of the development of concept mediation during second language acquisition is described.