Neutrino masses are not part of the standard model, but oscillation experiments have demonstrated convincingly that non-zero neutrino masses (and mixing angles) exist. Probably the simplest explanation for this experimental
fact is the seesaw mechanism, but many models for neutrino masses have been proposed in the literature. In this talk, I will briefly discuss the minimal seesaw and how electroweak scale seesaw might be tested in long-lived particle searches and then give an overview of non-minimal neutrino models,
where I discuss radiative models and models from higher-dimensional operators.