  Theories proposing a varying speed of light have recently been widely
promoted under the claim that they offer an alternative way of solving the
standard cosmological problems. Recent observational hints that the fine
structure constant may have varied during over cosmological scales also has
given impetus to these models. In theoretical physics the speed of light, $c$,
is hidden in almost all equations but with different facets that we try to
distinguish. Together with a reminder on scalar-tensor theories of gravity,
this sheds some light on these proposed varying speed of light theories.
