Researchers, policymakers, and practitioners agree that improving the content and delivery of teachers' professional development is essential to improving student achievement. But innovative solutions do not magically appear out of the mental soup of what educators already know about instruction and its improvement. While school districts are responsible for providing professional development opportunities for their teachers, their capacity to sustain high standards for teaching and learning often is limited by insufficient expertise and resources. Given limited internal capacity to construct dynamic professional learning opportunities, school districts increasingly are seeking partnerships outside the system. External coaching organizations are emerging as promising partners, offering a potential source of expertise that can augment what districts and schools might otherwise do to shape teachers' knowledge, skills and beliefs about content and their students as learners. In this article, the authors cites the various efforts made by several institutions to address their needs for external expertise.