This chapter addresses some key terms and distinctions that are essential background to chapters that follow. The term task is defined in the context of task-based language teaching (TBLT), and the role of the learner within this paradigm is problematized. Following this, a distinction is made between affective and conative variables, and these are variables positioned within the larger discourse of individual differences research in TBLT. Finally, a distinction is made between two complementary approaches to research (nomothetic and idiographic) as a basis for integrating the different perspectives, claims and suggestions for ongoing work discussed in the different chapters. Following this essential background, the respective parts of the book are introduced and a preview of the chapters contained in each is provided.