Mixed dark matter is also called hot + cold dark matter. The most abundant form of dark matter is cold dark matter, almost one fourth of the energy contents of the Universe. Neutrinos are the only known particles whose Big-Bang thermal relic should compose at least a fraction of Hot dark matter (HDM), albeit other candidates are speculated to exist. In the early 1990s, the power spectrum of fluctuations in the galaxy clustering did not agree entirely with the predictions for a standard cosmology built around pure cold DM. Mixed dark matter with a composition of about 80% cold and 20% hot (neutrinos) was investigated and found to agree better with observations. This large amount of HDM was made obsolete by the discovery in 1998 of the acceleration of universal expansion, which eventually led to the dark energy + dark matter paradigm of this decade.