Today, wireless sensor networks have become a key technology for different types of "smart environments", and an intensive research effort is currently under way to enable the application of wireless sensor networks for a wide range of industrial problems. The need for a cost-effective means for sensor localization eliminates a variety of options including GPS. Several approaches are available to determine the location of the sensor nodes. Most of these algorithms require extra hardware resulting in higher costs that is not feasible for large networks. In this book, an RF-based localization approach is presented that utilizes particle filters. Due to the availability cheap wireless transmitters with received signal strength indicators, the proposed approach provides an effective solution to the challenging problem of localization. A prediction algorithm is designed to overcome the complications caused by fast fluctuations in the received signal power due to the propagation channel. Particle filters are then utilized to estimate the position of the sensors. A major development that has been presented in this book leads to significant increase in the positioning accuracy.