  Neutron Stars (NSs) are compact stellar objects that are stable solutions in
General Relativity. Their internal structure is usually described using an
equation of state that involves the presence of ordinary matter and its
interactions. However there is now a large consensus that an elusive sector of
matter in the Universe, described as dark matter, remains as yet undiscovered.
In such a case, NSs should contain both, baryonic and dark matter. We argue
that depending on the nature of the dark matter and in certain circumstances,
the two matter components would form a mixture inside NSs that could trigger
further changes, some of them observable. The very existence of NSs constrains
the nature and interactions of dark matter in the Universe
