Mass and Mixing Angles of theτNeutrino

We examine the possibility that the $\tau$ neutrino is sufficiently massive to require it to be unstable ($m_{{\nu }_{\tau }}\gtrsim 50$ eV). A combination of experimental and astrophysical bounds requires a mass greater than 10 MeV. For larger masses, we bracket the lifetime and decay modes of ${\nu }_{\tau }$, and we give concomitant limits on the leptonic mixing angles.