This book traces and summarizes the author’s theoretical insights and empirical findings in the field of foreign language education. The volume explores themes such as individual differences in L1 ability and their connection to L2 aptitude and L2 achievement, L2 anxiety as an affective or cognitive variable, and the relationship between L1 and L2 reading. The book includes the author’s previously published works, presented together with newly written commentaries on those topics, as well as commentaries on new empirical work. It will be of interest to students and researchers in SLA, educational practitioners and language policymakers.