  We address neutron stars and black holes in alternative gravities, after
recalling their basic properties in General Relativity. Among the plethora of
interesting alternative gravities we here focus on an interesting set of
scalar-tensor theories. We discuss the phenomenon of spontaneous scalarization,
that is matter induced for neutron stars and curvature induced for black holes.
Along with other relevant physical properties, we address the quasi-normal
modes of these compact objects. In particular, we consider \textit{universal
relations} of neutron stars to largely reduce the dependence on the equation of
state, and we briefly address the shadow of black holes.
