Neutrino oscillations in dense neutrino media is a very nonlinear and rich phenomenon.
Such a dense neutrino gas could be found in very extreme astrophysical sites such as 
core collapse supernovae and neutron star mergers. Studying collective neutrino oscillations 
in the aforementioned settings is very essential since neutrinos could play a key role both 
in the dynamics and, in the nucleosynthesis. In this seminar, I will talk about our current understanding 
of this topic which has tremendously changed in the past few years.