The importance of incorporating second language acquisition (SLA) research into second language teacher education and classroom practice has been recognised (Ellis, 2005;Tarone & Allwright, 2005). However, this is a challenge as exemplified in task-based language teaching (TBLT), which closely draws on SLA research. The present study focuses specifically on one area of SLA, language input. By using a multimethod case study approach, it documents six Vietnamese EFL teachers' conceptions of input. The study generally showed that the teachers had a synthetic conception of input. Some contextual factors also constrained their provision of rich comprehensible input. The study provides insights into how teacher cognition is mediated by professional development, prior teaching experiences, and many other aspects of both present and past contexts (Borg, 2006). Specifically, the study justifies why integrating key SLA concepts into practice is challenging, and why teachers' conceptions must be considered in implementing innovations.Although task-based language teaching (TBLT) is strongly claimed to be a powerful approach because it aligns with how learners acquire a second language (Shehadeh, 2005), research has documented not insignificant obstacles to its implementation in Asian settings (Littlewood, 2007;Swan, 2005). This highlights the concern that externally developed innovations have often disregarded contextual factors. Given the widespread interest in and recognition of the importance of professional development in new and emerging language teaching methods and approaches, it is essential to reconsider possible ways of addressing this concern. Lightbown (2000) suggests that SLA researchers need to listen to what teachers are saying to appreciate their greatest areas of need in professional development and knowledge, and to understand the contexts in which they work. To do this means to understand teachers' conceptions.The present study approaches teachers' conceptions from a constructivist perspective, seeing teacher learning as the personal specific meanings teachers construe for knowledge, skills, or concepts, which in turn mediate their actions in practice. Teachers' conceptions not only interact with their classroom practice, but also are shaped by their own educational experiences, professional development experiences, prior teaching experiences and many