Over the past decade, research on the use of technology in the mathematics classroom has focused primarily on issues of student learning and engagement. In this article, we focus on middle grades mathematics teachers' use of The Geometer's Sketchpad, and study both the decisions they make about when to use technology, and their motivations for choosing certain technology-based tasks over others. Based on survey responses, we found that the strongest criterion for task selection was very high textbook fidelity. However, teachers also tended to select tasks according to other criteria, including the task's ability to address known student difficulties and to offer an alternative to physical manipulatives. These findings should help inform researchers involved in designing technology-based activities but, more importantly, they provide important insight into the ways actual classroom teachers implement technology-based lessons. (Contains 1 table and 7 figures.)