  In these lecture notes, the role of strangeness in relativistic astrophysics
of compact stars is addressed. The appearance of strange particles, as
hyperons, kaons, and strange quarks, in the core of compact stars is examined
and common features as well as differences are presented. Impacts on the global
properties of compact stars and signals of the presence of exotic matter are
outlined for the various strange phases which can appear in the interior at
high densities.
