Dams are part of human achievements that induce great benefits for society but also bear a potential risk to people, property and the natural environment. The risk of a dam rupture is extremely low and diffi cult to quantify accurately. The aim of 'Dam surveillance' (ICOLD Bulletin 158), is to help reduce these risks by early detection of an undesirable event. The objective of dam surveillance is to make a precise and timely diagnosis of the behavior of dams, in order to prevent undesirable consequences. Both the monitoring system and surveillance program has to be designed and should be able to detect any abnormal behaviour. 'Dam surveillance' (ICOLD Bulletin 158), emphasizes the following aspects: * Routine visual inspection * Special inspection * Checking and testing of Hydro-electromechanical equipment * Monitoring parameters and devices * Automation * Maintenance of ageing monitoring systems * Re-instrumentation of existing dams * Recent developments * Data management * Dam documentation management * Assessment of dam condition and behaviour * Assessment of routine dam safety monitoring programme * Prioritization of maintenance, remedial and upgrading works.