Over the past decade, the focus of investigation in individual differences (IDs) research has shifted from the utilization of large-scale questionnaire surveys toward the adoption of methodological diversity and development of new approaches to second-language (L2) communication (Dörnyei and Ryan [2015]. "The Psychology of the Language Learner Revisited." New York: Routledge.). One innovative approach to researching complex dynamic systems (e.g. individual difference characteristics such as motivation) is the 'idiodynamic method', which is developed to capture moment-by-moment fluctuations during L2 communication tasks. This review aims to examine the contributions that the idiodynamic methodology can make to individual differences in L2 learning. Focusing on three prominent areas in ID research (L2 willingness to communicate, language motivation, and language learning anxiety), the review examined 32 idiodynamically-informed studies published in the last decade. The findings indicate that the idiodynamic method -- as a powerful research tool -- could potentially contribute to investigating the dynamics associated with learner-related and teacher-related factors. The idiodynamic method is found to (1) encourage a reinterpretation of IDs, modeling them in terms of different timescales and changes in real time; (2) recognize the trajectories involved in learning-teaching behaviors; (3) highlight the interaction of communication traits and co-existence of stability and variability in the L2 learning system; and (4) quantify the variability in the ratings and the variation in IDs in real time communication. The review confirms the practical value of the idiodynamic methodology in L2 research and concludes with a brief discussion of implications of the methodology and suggestions for future studies.