Positive emotions can build cognitive and emotional resources. From this perspective, the consensus of opinion is that positive emotions contribute to “approach behavior” or “continued action”. That is to say, individuals experiencing positive emotions actively engage with their environment and participate in activities. This paper aims to address whether the Broaden-and-Build theory of positive emotions developed by Fredrickson may facilitate second language learning. In the light of this theory, it is argued that positive emotions can widen students' scope of attention, cognition and action and further produce a tendency toward activity engagement. In contrast, negative emotions reinforce the opposite tendency, restricting the amount of potential language input and accordingly narrowing the students' capacity for learning. The paper concludes that positive emotions are closely associated with higher levels of students' engagement and negative emotions with lower levels of engagement. In general, therefore, it seems that second language teachers should go beyond a focus on the reduction of negative emotions towards a focus on the enhancement of positive emotions.