The six papers in this issue address, in different ways, teacher education 1 programs and initiatives for practising teachers. While the necessity of ongoing professional learning across all the professions is a given, we argue that it is of increasing importance in teaching in the current era. The shift in many countries in the 21 st century to the standardisation of teaching means that teachers and school leaders are required to account for their teaching practices in ways to which they were not previously called. In Australia, for example, engaging in professional learning represents one of seven standards of practice (Australian Institute for Teaching and School Leadership (AITSL), 2011) and, in the United Kingdom, the Teachers' Standards (United Kingdom Department of Education, 2011) require teachers to take responsibility for developing their teaching skills through appropriate professional development. The introduction of these types of accountability measures has led to changes in many quarters in the ways in which professional learning is conceived and delivered, as well as to increased scrutiny from the educational and broader communities of the efficacy of teacher professional learning measures (see, e.g., Darling-Hammond, Chung Wei, & Andree, 2010; Productivity Commission, 2017). The Australian Productivity Commission (2017) recently noted that "raising student performance depends on the capabilities and practices of teachers and principals" (p. 90) and recommended that Australian governments should "improve the skills and effectiveness of the existing teacher workforce, with comprehensive professional development initiatives and other mechanisms, supported by evidence that these are genuinely effective" (p. 15). From a similar standpoint, AITSL (2012) developed the Australian Teacher Performance and Development Framework at the start of the decade, with a view to creating a performance and development culture in all schools, "characterised by a clear focus on improving teaching as a powerful means of improving student outcomes" (p. 2). While we acknowledge that these types of claims and recommendations are subject to debate, as are the ontological and epistemological stances from which they are generated, they nonetheless represent commonly-espoused expectations around professional learning and its outcomes, to which teachers and teacher educators are currently beholden. It is within this context that we consider and problematise the concept of teacher professional learning. At the level of definition, it is important that we shift away from the notion of "professional development" because of the implied lack of agency that this term evokes: teachers cannot be developed by external agents and measures; rather they require opportunities to develop and enhance their practice through professional learning in its myriad formsworkplace learning, communities of practice learning, everyday learning, etc. Powerful professional learning promotes sustained growth in the learner, particularly through collaborat...