This edited book brings together ten empirical papers reporting original studies investigating different facets of individual variation second language learning and teaching. The individual difference factors covered include, among others, motivation, self, anxiety, emotions, willingness to communicate, beliefs, age, and language learning strategies. What is especially important, some of the contributions to the volume offer insights into intricate interplays of these factors while others attempt to relate them to learning specific target language subsystems or concrete instructional options. All the chapters also include tangible implications for language pedagogy. The book is of interest to both researchers examining the role of individual variation in second language learning and teaching, teacher trainers, graduate and doctoral students in foreign languages departments, as well as practitioners wishing to enhance the effectiveness of second language instruction in their classrooms.