This chapter includes the findings and results of dedicated research and development in the area of location determination in mobile computing environments using wireless infrastructures and other aiding sensors such as inertial sensors and dead reckoning. The theoretical formulation of the location determination problem is explained followed by a background and state of the art in location technology and current limitations and challenges. Different wireless localization technologies are analyzed theatrically using Cramer-Rao Lower Bound (CRLB) Variance analysis and practically using real experiments. The problem of wireless propagation modeling and radio maps construction and maintenance are addressed using wide range of deterministic and probabilistic estimation approaches. The theoretical justification is verified by extensive experimental demonstration. Integration of the wireless infrastructures with onboard sensors associated with current modern mobile devices are studied using Kalman Filtering (KF) and Particle Filtering (PF) supported by a comparison between these two common filtering techniques. The chapter concludes with a section about future trends and new research tracks that are expected to shape the localization and tracking landscape of the next few decades.