The main objective of this thesis is to analyse the history of one of the oldest public transport companies in our country: Compañía del Tranvía de San Sebastián (San Sebastian Tramway Company), founded in 1886 and at present the company that still owns urban services in Guipuzcoa’s capital city. To this end, the thesis analyses the company’s technological changes from the mule tram to the bus, including the electric tram and the trolleybus, as well as its financial evolution, income and expenses, demand or the transition from private to public company. All that without forgetting other aspects directly connected with the activity of these types of companies, such as the situation of its workers or the implications for the urban development of the city, whose stamp on San Sebastian landscape is still clear.