  We give an overview of the current status of keV sterile neutrino Dark
Matter. After a short introduction, we start by a general discussion of
non-thermal production of Dark Matter, which applies to the three most commonly
discussed mechanisms to produce sterile neutrino Dark Matter in the Universe:
non-resonant, resonant, and decay production. The main goal in each case is to
compute the momentum distribution function $f(p,t)$, which incorporates the
full information about the Dark Matter setting under consideration, at least in
what concerns its cosmological aspects. While some difficulties lie in the
actual computation of this quantity, it is decisive to obtain bounds from
cosmic structure formation, which turn out to be the most crucial ones to
distinguish different types of production. We will introduce these bounds and
we put the resulting limits into a proper context, thereby illustrating that a
significant amount of relevant parameter space is available, part of which is
testable in particular by Lyman-$\alpha$ data.
