Willingness to communicate in a second language (L2 WTC) is a learner's volitional participation in oral communication using L2. Previous research has expended considerable attention to the stable, trait-like disposition of learners' L2 WTC, while less focus has been accorded to the complex nature of variations in L2 WTC on multiple timescales. Using dynamic systems theory, the present article examines the complex nature of variations on three timescales: during conversation, between classes and over time. The data were obtained from six postgraduate students through structured classroom observations, learners' diaries, stimulated recalls and biographic questionnaires. The findings show that while variations in L2 WTC within and between the classes were influenced by situational variables, such as interlocutors, topic and perceived opportunity, variations over 14 classes were strongly affected by enduring factors, such as personality and trait-level motivation. Introverted learners showed dependency on their interlocutors to provide them with opportunities for L2 use. Conversely, extraverted learners proactively exploited opportunities to use L2 regardless of the nature of topic of discussion and the behaviour of interlocutors. The study also discusses a number of implications for language teaching and teacher education.