In this article we address the "highly qualified teacher" provisions of the No Child Left Behind (NCLB) Act of 2001. We argue that the provisions' intent is important and achievable, and we outline critical research on the issue of which teacher qualifications matter for student learning. Three questions frame the discussion: Does teacher quality matter? What qualifications make a difference? How does teacher certification matter? We address the issue of ensuring highly qualified teachers for all children, providing examples of policies that have enabled states and districts to recruit and retain qualified teachers. Finally, we propose a set of federal teacher initiatives that can support such policies nationwide. (Contains 11 notes.)