In this project, a reliability-based classification of the load carrying capacity of existing concrete bridges is carried out. Firstly, a state-of- the-art assessment of existing concrete bridges is presented. Some topics are discussed as for instance the different between assessment and design of bridges, analytic or experimental approach, as well as the procedures and methods of assessment according to European research projects and national codes and guidelines. Then, the stochastic modelling is presented, considering load modelling and material modelling. In the load modelling, the permanent load as well as the variable load, namely traffic load, are modelled. In addition, concrete as well as non-prestressed reinforcement steel are modelled. The model uncertainty is considered also. Once the stochastic modelling is established, a reliability analysis is carried out. Then, these reliability results, measured by the reliability index, β , are improved by different types of updating, which are an updating by proof load tests and updating by test results re- lated to the material parameters, with the aim to avoid costly rehabilitation or demolition of a bridge that in reality fulfils the safety requirements. Finally, an order of implementation of these updating methods is proposed and the recommended future work is mentioned.