Ten native Chinese-speaking children and adolescents who immigrated to the United States between ages 5 and 16 were studied for 3 years. The changes in their language preferences, language environments, and proficiency in English, their second language (L2), as well as Chinese, their first language (L1), were measured quantitatively and qualitatively. Participants with arrival ages of 9 or younger switched their language preference from L1 to L2 within the first year, were exposed to a significantly richer L2 than L1 environment, and became more proficient in L2 than in L1. The older participants maintained their preference for L1 across the 3 years, were exposed to a significantly richer L1 than L2 environment, and maintained L1 as the more proficient language. Interactions among L1 proficiency, peer interactions, social abilities, and cultural preferences jointly influenced the dominant language switch or maintenance processes.