The book is renowned for its novel approach combining psychology, applied linguistics, and cognitive science as well as for its extensive examination of the state of individual differences research. Beyond a basic field review, every chapter explores the theoretical and empirical limits of modern methods. This volume confirms the significance of personal variance in L2 learning. The four main sections of the book, each of which concentrates on a different set of cognitive variables, are age, intelligence, aptitude, and affect (Part I); memory, attention, and noticing (Part II); learning strategies, metacognition, and self-regulation (Part III); L2 skills, learning challenges, and anxiety (Part IV).