Monitoring of bridges under construction. Supervision and measurement have always played a central role in the construction industry in order to understand the real behaviour of structures. However, through the development of numerical methods in the recent decades it was attempted to answer the questions in planning and execution of constructions almost completely numerical, so that the demand for measurements has fallen. The numerical methods, however, involve the danger of relying almost blindly on the results because of the achievable degree of detail of the models and the available calculation possibilities. In the recent past a return to metrological methods can be observed, which can partly be explained by questioning this trend. In particular in the course of construction work, either on the building itself or in the vicinity of it, the actual boundary conditions are very difficult to model because of the constantly changing construction conditions, the very scattering and sometimes unknown effects as well as the temporal development of the material properties. In these situations, measurements provide excellent opportunities to resolve existing uncertainties in numerical models or to detect critical situations early on. In this paper the different applications for measurements are categorised and presented by means of examples. The aim is to show in which cases metrological monitoring may be necessary or useful and which aspects are of importance in the interdisciplinary implementation of the supervision task.