The research work that is presented in this thesis aims at mapping out the various mechanisms which control the process of steel corrosion in concrete. The process of corrosion is illustrated with a schematic model where the service life is divided into a period of initiation and a period of propagation. The time up to the initiation of the corrosion process is determined by the flow of penetrating substances into the concrete cover and by the threshold concentration for corrosion to start. Theoretical models have been produced to approximate the time of initiation. The rate of corrosion in the propagation period can be described by the relative humidity in the concrete and the mean temperature of the structure. Different relations between these factors and the rate of corrosion have been put up for different initiation mechanisms. The final state, cracked concrete covers, reduced cross-section area of the steel etc. is discussed in the model. Other important factors, which have not been deal t with in the model, are also discussed. A method for predicting service life of concrete structures is presented. The report also includes applications in various forms of the method. The report is concluded with a documentation of laboratory investigations carried out by the author.