Erice: INTERNATIONAL SCHOOL OF NUCLEAR PHYSICS, 47th COURSE

In this talk I will review the most prominent anomalous results in neutrino oscillation experiments, which may be interpreted as hints towards the existence of extra sterile neutrino states beyond the three known active ones. After discussing the individual findings, we will put emphasis on the synergies between different classes of experiments, showing how the interplay among solar, atmospheric, reactor and accelerator data pose challenges to a common interpretation of all data under the sterile neutrino paradigm.