The aim of the current study is twofold: to examine the effects of input on bilingual adolescents’ long-term second language (L2) outcomes in a minority/foreign language context; and to understand the interaction between input and other potential predictors of L2 outcomes, specifically environmental variables, learners’ motivation and language learning aptitude. Participants included 97 Mandarin–English bilingual adolescents in Taiwan who learned English as an L2 between the ages of two to eleven. All participants completed a listening comprehension and a story-telling task in English and two standardized language learning aptitude tests. Participants and their parents filled out a detailed questionnaire providing information about family demographics and in-class and out-of-class L2 input. Correlation and multivariate regression analyses revealed that input played an important role in long-term L2 listening comprehension outcome, but not in speech production outcomes. The results also showed that environmental variables and language learning aptitude significantly predicted long-term L2 listening comprehension and speech production outcomes. Finally, out-of-class L2 input outweighed instructional input and current input outweighed early input. Since most previous research on the role of input in long-term L2 outcomes was conducted in a majority/societal language context, the present study contributes to the topic by specifying the effect of input in L2 acquisition in a minority/foreign language context.