Abstract: The tau neutrino is the Standard Model particle with the fewest identified events. Most tau-neutrino interactions cannot be distinguished from other flavor neutrino interactions. This is due to the large mass of the tau, which causes the production threshold to open up at a few GeV, and the prompt tau decay. The study of astrophysical neutrinos provides important clues about cosmic particle accelerators. In particular, the tau neutrino fraction at Earth is directly translatable to the source flavor composition and can constrain source production mechanisms. For neutrinos of energies greater than ~100 TeV, IceCube becomes sensitive to the identification of tau-neutrino charged current interaction on an event-by-event basis via the double bang channel. This channel consists two energy depositions one from the tau production and the other from the tau decay. With no significant tau neutrino production expected at the source, IceCube is the first experiment able to observe neutrino oscillations over cosmological baselines. I will present and discuss recent measurements of the astrophysical flavor composition.