Willingness to communicate (WTC) used to be studied as a relatively stable, trait-like predisposition; however, recent attention has been shifted to more dynamic, state-like components of WTC, i.e. possible fluctuations in state WTC over time. This research investigates variability and stability in both trait and state WTC. It particularly focuses on within-person variability in state WTC, which may lead to stable between-person differences, and situational antecedents that can either promote or hinder state WTC in L2 classrooms. Published research on state WTC was systematically reviewed, and frequently reported situational antecedents of state WTC were organised into a framework composed of three inter-linked layers: situation cues, situation characteristics, and underlying dimensions. Two high-density repeated measurement studies conducted in English classrooms in a Chinese university, investigating whether, how and why state WTC varied during a semester (Study 1) and during a lesson (Study 2), respectively. The two studies found that (a) state WTC varied both within a lesson and across different lessons during a semester; (b) within-person variability in state WTC was systematically related to the situational antecedents proposed in the framework (e.g. support, task-importance, task-interest, etc.); and (c) systematic within-person variability in state WTC predicted English learning performance, particularly in terms of communicative competence. This research provides novel insights into how within-person variability in state-like variables can be studied, and the proposed framework can be used as guidance for future research on state WTC and its situational antecedents. This research also suggests practical strategies for educators and language L2 teachers who would like to facilitate student state WTC by systematically shaping classroom learning situations
