Reliable estimates of population parameters and their trends are necessary for effective management and conservation actions, especially for endangered species such as wolves in most European countries. Under the Habitat Directive 92/43/CEE, all countries are required to monitor the status of their endangered populations. The ultimate goal of population monitoring is to detect a change in both magnitude and direction for one of the population parameters. We discuss the importance of wolf populations monitoring in Europe, giving examples from the contributions of this theme issue, and we highlight the technical challenges of transboundary monitoring and of preventive measures implementation.