Modelling, Simulation and Analysis of Tunisian Electricity System; The Thesis is concentrated on the modelling of the actual power generation system and high voltage transmission and distribution infrastructure of Tunisia with the perspective of optimization of the power flow (OPF). The backbone and starting point of the project was a database of the power system inventory of the country. Because of the lack of such data, a big part of the work was concentrated on the data mining and validation of the collected data through reliable sources or information published by authorities. The data must involve all present power plants with their generation capacity, number of production units and fuel type as well as the location of the power stations and the present levels of tension.