The project Status and Conservation of the Alpine Lynx Population (SCALP) is an ongoing program aiming to co-ordinate the lynx monitoring and propose conservation activities in the Alps. The SCALP project was initiated from several active lynx researchers as an informal group in the early 1990s – twenty years after the reintroductions in Switzerland, Italy, Slovenia, and Austria. To propose adequate management measures, a sound monitoring of the Alpine lynx population needs to be in place. In the early 1990s the first efforts were made to put all available data on lynx presence together. The least common denominator of data collection in the Alps was – and still is – the compilation of direct and indirect signs of lynx presence. To standardise the interpretation of the data collected, SCALP experts agreed on a categorisation of occurrence records, where each record is evaluated retrospectively whether it can be verified for correct species identification and whether it has been verified for correct species identification. Therefore, for the monitoring of the lynx throughout the Alps in the frame of the SCALP surveys, the collected data are classified in three categories according to the following SCALP criteria: Category 1 (C1): "Hard facts", verified and unchallenged observations; Category 2 (C2): Observations controlled and confirmed by a lynx expert (e.g. trained member of the network); Category 3 (C3): Unconfirmed category 2 observations and all observations such as sightings and calls which, if not additionally documented, by their nature cannot be verified. The SCALP criteria allow to both combine and distinguish reliable and only partly reliable data for a better interpretation of the actual distribution.