Supporting a productive discourse is an important element of reform teaching, as it gives students opportunities to understand mathematical reasoning. In this study, the practices of an expert seventh-grade mathematics teacher are described to illustrate how she created and sustained a genuine mathematical discourse environment during the teaching of the integers unit. The results indicate that the teacher's actions to promote discourse can be collected under four main practices that support students' understanding and exploration. These practices are analyzed using the theory of teaching in context, which uses beliefs, goals, and knowledge to explain the rationale behind the teacher's actions. (Contains 3 figures and 1 note.)