  Theories that attempt to unify the four fundamental interactions and
alternative theories of gravity predict time and/or spatial variation of the
fundamental constants of nature. Different versions of these theories predict
different behaviours for these variations. In consequence, experimental and
observational bounds are an important tool to check the validity of such
proposals. In this paper, we review constraints on the possible variation of
the fundamental constants from astronomical observations and geophysical
experiments designed to test the constancy of the fundamental constants of
nature over different timescales. We also focus on the limits that can be
obtained from white dwarfs, which can constrain the variation of the constants
with the gravitational potential.
