The IceCube Observatory has been detecting neutrinos with energies exceeding hundreds of TeV,
whose origin is currently a major mystery. Recently, a real-time alert of a high-energy neutrino detection triggered
extensive electromagnetic follow-up observations, allowing the identification of a blazar flaring
in gamma rays as a promising candidate source. We discuss various ways to interpret these observations
in the context of our current understanding of blazars, and address the implications for the physics of jets
in active galactic nuclei and production of ultra-high-energy cosmic rays.
The importance of further observational efforts, especially in X-rays and gamma rays, will be highlighted.