Games can both generate excitement among students and motivate them to participate in mathematics. Although games have been used primarily to "review" mathematical concepts at the middle school level, games should, and often do, have other instructional purposes. When teachers use mathematical games as an instructional strategy, they are giving students opportunities to actively engage with the mathematics. The authors critically evaluated the appropriateness and effectiveness of various mathematical games and sought specific criteria to help them select games that would promote mathematical thinking and reasoning. After reflecting on students' interactions and discussions during game play, they identified specific guiding questions to help with the selection and implementation of games. In this article, they describe one game, Product Bingo, and how it played out in one middle school classroom. They then use that game to introduce three guiding principles that can help middle school mathematics teachers as they use and reflect on implementing games in the classroom. A bibliography is included.