Due to uncertainties in the ground model and the spread of geotechnical properties, prediction of the exact system behaviour of underground structures is difficult in many cases. In order to manage this problem, the so-called observational approach is often applied. Monitoring plays an important role to verify or falsify design assumptions, to adjust excavation and support measures to the actual conditions and to assess the stability of the system. For the management of the residual risk a geotechnical safety management plan is implemented. The OeGG has recently published a handbook summarizing the state of the art in tunnel monitoring and geotechnical safety management.