Due to the flexibility and mobility of wireless technologies; Bluetooth, Zig-bee, RFID, WiMAX etc. have become most commonly used medium of wireless communication. Although the demand of these technologies is rapidly increasing all over the world, very few of us are aware about the security issues related to them. A number of attacks is possible to make illegal access to our system if we do not know how to protect our system from intruders. This book focuses on security threats and countermeasures of Bluetooth, MANET and WiMAX. The readers will get to know about different types of attacks as well as preventive mechanisms. Some research questions are also identified that may be interesting to those who want to go for further study.