Neutrino oscillation experiments have firmly established that neutrinos have tiny but non-vanishing masses, and that the different neutrino flavors mix.
In this talk, it will be argued that as an alternative to the usual seesaw mechanism, small Majorana neutrino masses could have a radiative origin. Some specific models of loop
induced neutrino masses will be presented, and their main phenomenological aspects will be discussed.
If the scale of lepton number violation is close to the electro-weak scale, it will be possible to test directly these models in a large variety of experiments.