There has been a growing interest in SLA in studying second language (L2) writing development and change from a complex perspective, taking into consideration the full combination of learning processes, learners and contexts of learning. Thus, the research reported here applies a Dynamic Systems Theory (DST) approach to investigate L2 writers" sense of self-efficacy. Although self-efficacy is usually viewed as task-specific, and therefore measured in relation to specific situations, such an approach tends to lead to the production of cross-sectional research looking at one time and one context only. This study moves instead to consider L2 writing self-efficacy as a complex dynamic system that evolves in response to the environment as well as internal re-organisation. Changes in L2 learners" writing self-efficacy were traced over a six-week period through the use of writing self-efficacy questionnaires and introspective journals. Results suggest that L2 writing self-efficacy is best perceived as a dynamic, rather than a fixed, construct, and as complex rather than one-dimensional. Students" perception of their abilities to write is changeable, decentralised, open to influences from the environment and from other external factors, displays non-linear development and tends to settle down in attractor states.