Every learner is an individual who brings a unique configuration of characteristics and experiences to language learning. A robust research tradition examines variation among individuals which includes prominent topics such as memory, motivation, anxiety, and willingness to communicate, to name a few (Li et al., 2022). Conative and affective ID variables can fluctuate a great deal across a group of learners during task performances, but more importantly to the present chapter, there also can be substantial variation within individuals over time. Unfortunately, task-based language teaching (TBLT) research typically ignores this latter type of variation and by doing so is missing an important part of the puzzle that is task-based learning. Research methods are needed to study intra-individual variation in addition to inter-individual variation. The present chapter will address this need by providing practical guidelines for using the relatively new idiodynamic method to capture moment-by-moment fluctuations in specific learners’ conative (e.g., WTC, motivation) and affective (e.g., emotions) dispositions during second language (L2) task performance.