Against the background of immense costs of repair or replacement of concrete structures degraded by reinforcement corrosion, a strong interest in industry and research can nowadays be found in the underlying processes and in possibilities to influence them. As a part of the reinforcement corrosion circuit, the resistivity of concrete is a decisive material parameter with regard to corrosion propagation, which itself is a time-dependent process of many years of length. For this reason, a picture of the long term behaviour of the resistivity of concrete could be of great value. This paper presents resistivity data of concrete specimens up to an age of 17 year. An investigation was carried out of their development throughout the years in dependence of all main aspects influencing the magnitude and the development of the resistivity (climate, cement type, water/cement-ratio).