Sterile neutrinos: from cosmology to experiments

We analyze the oscillation signals generated by one extra sterile neutrino. We fully take into account the effects of the established oscillations among active neutrinos. We analyze the effects in solar, atmospheric, reactor and beam experiments, cosmology and supernov\ae. We analyze the impact of the LSND anomaly on cosmology showing, in the full 4 neutrino context, that it is not compatible with standard cosmology. We identify the still allowed regions of the parameter space, outlining which are the future experiments which can improve the bounds.