Wireless student response systems—“clickers”—address two of the oldest and most fundamental challenges in teaching: how to engage students and how to determine if they are learning what you are teaching. Clickers are relatively low cost and easy to use. Data show that when they are used well in large lecture classes, clickers increase the engagement of students and improve their learning. This is particularly true when students are encouraged to debate answers with their neighbors before answering. Students overwhelmingly like using clickers and believe that they increase their learning. Clicker use also increases class attendance. Like any technology, it is possible to misuse clickers. Common mistakes made by new clicker users and how to avoid them are described. As of 2006, clicker technology is changing in a way that favors radio (RF) rather than infrared transmission. Those installing clicker systems should profit from these changes.