Current curriculum initiatives in mathematics call for the development of classroom communities that take communication about mathematics as a central focus. In these proposals, mathematical discourse involving explanation, argumentation, and defense of mathematical ideas becomes a defining feature of a quality classroom experience. In this article, the authors provide a comprehensive and critical review of what it is that mathematics teachers actually do to deal with classroom discourse. Synthesizing the literature around a number of key themes, the authors critically assess the kinds of human infrastructure that promote mathematical discourse in the classroom and that allow students to achieve desirable outcomes. From the findings, they conclude with implications for teachers. (Contains 1 note and 5 figures.)