Use of mobile computing devices such as laptops, PDAs, and Wi-Fi enabled phones is increasing in the workplace. As the usage of corporate 802.11 wireless networks (WLANs) grows, network performance is becoming a significant concern. We have built DenseAP, a novel system for improving the performance of enterprise WLANs using a dense deployment of access points (APs). In sharp contrast with wired networks, one cannot increase the capacity of a WLAN by simply deploying more equipment (APs). To increase capacity, the APs must be assigned appropriate channels and the clients must make intelligent decisions about which AP to associate with. Furthermore, the decisions about channel assignment, and associations must be based on a global view of the entire WLAN, rather than the local viewpoint of an individual client or AP. Given the diversity of Wi-Fi devices in use today, another constraint on the design of DenseAP is that it must not require any modification to Wi-Fi clients. In this paper, we show how the DenseAP system addresses these challenges, and provides significant improvements in performance over existing WLANs.