  The chameleon mechanism is a way to give an effective mass to a light scalar
field via field self-interaction and interaction with matter. We study this
mechanism in models in which the couplings are field dependent and find that
the properties are very different from the case of constant couplings. The
consequence of a runaway potential for the radion field in brane world
scenarios and whether the radion can play the role of dark energy is
investigated. The cosmological evolution during the inflationary epoch, the
radiation and the matter dominated epochs are discussed as is the compatibility
of the radion field with local tests of gravity.
