Although research into language teacher learning and cognition and teaching innovations oriented to communicative tasks has been abundant, little has addressed EFL teachers’ learning and conceiving of SLA principles underlying task-based language teaching. The study reported in the present thesis aims to fill this gap, specifically investigating teachers’ learning and conceiving of the notions of rich comprehensible language input, and authentic output and interaction, referred to as ‘SLA facilitating conditions’. The study explores three issues: teachers’ conceptions of the SLA facilitating conditions based on their practices in the tertiary English classroom; teachers’ perceptions of implementing the conditions, including factors affecting the implementation; and teachers’ perceived learning or change as a result of the process. Data for the study were obtained from six Vietnamese EFL lecturers who voluntarily participated in two short professional development workshops focusing on language input, and output and interaction. The data collection process was cumulative, beginning with pre-workshop interviews, followed by collection of lesson plans, lesson-based interviews, reflective writing, observation of lesson recordings, and a questionnaire. Analysis and interpretation followed a process of triangulation, and drew on the author’s knowledge of the context and the teachers’ backgrounds. The results showed that the six teachers held contextualised conceptions of language input, and output and interaction. Although they believed that these conditions are important for language learning, their conceptions based on their implementation of the conditions reflected a synthetic product-oriented view of language learning and teaching. The teachers demonstrated an accommodation of the notion of comprehensible input into their existing pedagogical understanding, and revealed a conception of language output oriented to accuracy and fluency of specific target language items. Tasks and activities for interaction were mainly to provide students with contexts to use the target language items meaningfully rather than to communicate meaning. Most teachers delayed communicative tasks until their students were acquainted with the language content of the day. Such conceptions and practices had a connection with both conceptual/experiential and contextual factors, namely their prior training and experience, time limitations, syllabus, and students’ characteristics. The study also showed that although the teachers’ perceptions of the feasibility of promoting rich language input and authentic output and interaction were neutral, they thought promoting these conditions was relevant to students’ learning, congruent with their pre-existing beliefs about teaching English, and this granted them a sense of agency. The teachers also reported they became more aware of input, and output and interaction in teaching, confident, and purposeful in actions, and some reported a widened view of English language teaching. The study confirms that teacher learning and cognition is conceptually and contextually conditioned (Borg, 2006). In terms of this, it provides a model of how EFL teachers’ learning SLA is constrained by prior pedagogical beliefs and contextual conditions. In conjunction with previous research, the study provided evidence to suggest that communicative and task-based language teaching would appear to run counter to existing beliefs about teaching and practical conditions in Asian EFL situations. This lends support to a more flexible organic approach to employing tasks, perhaps considering the extent to which and in what ways communicative tasks are pedagogically useful to the EFL classroom. An implication is that for any new approaches like task-based language teaching to be incorporated into teachers’ existing repertoire, teachers’ conceptions of language input and interaction, and the conceptual and practical constraints influencing their thinking and practice should be considered and addressed. In a broader sense, approaches to teacher education and development should take a constructivist perspective on teacher learning, taking into account the local context of teaching and teachers’ existing cognition.