Sterile neutrinos of keV scale are a well motivated candidate for Warm Dark Matter. I'll review the cosmological and astrophysical implications of keV sterile neutrinos. Then, I'll discuss the current models present in the literature, that are able to explain a sterile mass pattern with one neutrino at the keV scale and the other two considerably heavier. Finally, I'll present a new production mechanism for keV sterile neutrino Dark Matter from the decay of a frozen-in scalar.