Individual learner factors play an important role in how a task is performed. This requires a perspective that draws on the theory and research that addresses the psychology of the learner – what we call the psychological perspective on TBLT. Chapter 5 surveys the large body of research on the role of cognitive aptitudes (including working memory) in mediating the effects of different instructional tasks on language performance and acquisition. The chapter will also discuss the influence of affective factors such as motivation and language anxiety on task performance and outcome. A key focus of this chapter is how these psychological variables mediate the performance of a task and the learning that results.