Abstract. The purpose of the diploma thesis is the implementation of positioning and tracking methods for mobile users, based on wireless networks. In order to achieve our goal, we exploit general purpose wireless networks such as the 802.11 networks, the GSM network, etc. The fundamental idea is the utilization of every kind of Access Point (AP) as a beacon. While we are not requiring an active connection to the wireless network, we are able to provide positioning and tracking services. The accuracy achieved and provided by our service can be comparable to GPS. For example, almost all of us own a home based wireless network. This network transmits signal constantly. The transmitted signal can be received by anyone even if the network services are restricted. Our techniques are complementary of existing methods (such as GPS, A-GPS), but can fully replace them under certain circumstances. Our purpose was to seek for solutions regarding a series of problems including the inherent coverage problems (e.g. indoors positioning/tracking), user-friendly concerns (e.g. discrete devices), autonomy concerns (e.g. increased energy consumption due to a usage of a discrete GPS device) and security issues (e.g. third-parties acquiring knowledge regarding a user's position).of GPS. The implementation and the experimental evaluation of the most important algorithms mentioned in the literature was our main purpose, but we also extended them by incorporating new notions and techniques. In order to be more precise, we can summarize our contribution to the following (a) expand indoor techniques in order to use them in outdoor environments, (b) introduce map matching techniques as a motion model, (c)introduce map matching techniques in order to smooth and improve the estimations and, (d) introduce improvements concerning the error measurement when motion is performed on a road network or a graph.