Researchers have looked into the role of individual differences in second language learning and found that differences between learners in areas such as language aptitude, language learning motivation and exposure to the language influence second language learning. Most of this research concerned adults. Far fewer studies have addressed the role of individual differences in second language learning of young learners. As second language learning programmes tend to start earlier than before and children are nowadays frequently exposed to a foreign language in social settings such as online games and social media, studying the role of individual differences in young learners can contribute both to SLA-theories and to evidence-based L2 education. This book discusses recent findings concerning the role of individual differences in language learning in young learners. The chapters in the book concern different topics linked to internal individual differences such as language aptitude, motivation, attitude and external individual differences such as exposure and type of instruction, the relative contribution of internal and external factors to language learning, and the interplay between the two types of individual differences.