Neutrinos decaying on timescales which are shorter than the age of our Universe can relax cosmological neutrino mass bounds. We categorize all possible invisible neutrino decay modes in terms of particle content and neutrino decay final states. Our analysis shows that 3-body invisible neutrino decays are highly constraint, whereas 2-Body decays can significantly relax neutrino mass bounds. Finally, we discuss model building considerations to develop models which can trigger such decays.