The author clarifies the nature of expertise in language teaching, its development, and how teachers employ it. This book is the first detailed study of what expertise in language teaching consists of and how it develops in language teachers. Exploring the classroom practices of her subjects in four illuminating case studies, Tsui succeeds in clarifying the nature of expertise in language teaching, the factors that shape and influence its development, and how teachers employ their expertise in teaching. In the process, the author critically examines an extensive literature on teacher cognition and shows how teachers' theories, knowledge, experience, and goals shape their classroom practices and their ability to move from novice to expert.