Second language learning (L2) is a multifaceted phenomenon whose process and product are greatly affected not only by factors related to experience (e.g., how L2 learners have practiced the target language), but also by those which are learner-internal (e.g., to what extent they are talented at L2 learning). In this lecture, we will review what characterizes linguistic and individual difference profiles of “successful” adult L2 learners of English in classroom and immersion settings. In particular, I would like to introduce an emerging paradigm which states that one’s pre-existing auditory precision (i.e., having a good ear) could be one important factor for explaining the degree of success not only in child L1 acquisition but also in post-pubertal L2 learning. Interfacing psychology, education, and hearing research perspectives, I will highlight a range of questions that these studies have brought up, and invite the audience to critically discuss how we can maximize the speed/attainment of L2 learning by designing most effective and efficient methods of instruction (e.g., training both language and hearing). I will share my/students’ latest research projects and findings as well.