The development pace of location tracking research is highly tied up with the advancement of wireless sensor network (WSN) and wireless technologies. As sensor nodes in WSN became smaller and stronger, the ability of processing information and managing network operation also became more intelligent. This can be observed from the application of tracking from coarse-grained to fine-grained advancement. In coarse-grained tracking such as (Zhao, et al., 2003), the location of target is just detected by two or more sensor nodes along the movement path of the target. The coordinate of the tracked target is then determined by averaging the location coordinates of those sensor nodes which are able to detect the target. Using this approach, the accuracy and resolution of location estimation is affected by the density of sensor nodes in the area. In fine-grained tracking such as (Smith, et al., 2004), three or more sensor nodes are responsible to track the target in the area. Instead of just detection, the distances between the target and the sensor nodes are measured. The determination of distance between two entities is called “ranging”. Using the measured distances, the exact location coordinate of the target can be computed by angulation or lateration techniques (Hightower, et al., 2001). Therefore, increasing the node density of the area does not really increase the accuracy of location estimation. It rather depends on the accuracy of the ranging method. This chapter presents the authors’ research investigation of developing an indoor tracking and localization system. The experimental system was tested and achieved in the laboratory of Dongseo University for supporting author’s PhD studies. The thesis (Pu, 2009) provides further technical details for the design and implementation of the tracking system. For the ease of reading, this chapter was organized as follows: section 1 gives overall fundamentals of location tracking systems, from every aspect of considerations. Section 2 analyzes the nature of wireless ranging using received signal strength indicator, especially for the case of indoor signal propagation and ranging. Section 3 provides the complete flow of designing and implementing indoor location system based on received signal strength. Finally, section 4 concludes the whole work. 11