In recent years there has been a dramatic rise in interest and early adoption of blended learning to improve the educational experiences of students. A great amount of work has been done to codify approaches, with tools and resources emphasizing the structural components of new models, such as the configuration of physical learning space, use of time, distribution of staff, and applications of technology. While there is widespread recognition that great in person teaching remains essential within these structures, there has been less exploration of the human factors and effective practices that make them successful. Schools and districts are asking for more support for understanding teachers' new roles and effectively supporting them in transitioning to new models of teaching and learning. To respond to this need, iNACOL and The Learning Accelerator (TLA), two organizations committed to helping educators succeed at adopting and implementing blended learning at scale, assembled a national committee of blended learning practitioners, thought-leaders, and experts to explore one critical question: What are the key characteristics of teachers in successful blended learning environments? Over the last year, this committee worked together to review existing practices and research (including an earlier framework developed by TLA), to develop emerging hypotheses with each other and then field-test them with a broader set of external stakeholders. This process culminated in the development of the work presented here, the "iNACOL Blended Learning Teacher Competency Framework."