  We show that the chameleon scalar field can drive the current phase of cosmic
acceleration for a large class of scalar potentials that are also consistent
with local tests of gravity. These provide explicit realizations of a
quintessence model where the quintessence scalar field couples directly to
baryons and dark matter with gravitational strength. We analyze the
cosmological evolution of the chameleon field and show the existence of an
attractor solution with the chameleon following the minimum of its effective
potential. For a wide range of initial conditions, spanning many orders of
magnitude in initial chameleon energy density, the attractor is reached before
nucleosynthesis. Surprisingly, the range of allowed initial conditions leading
to a successful cosmology is wider than in normal quintessence. We discuss
applications to the cyclic model of the universe and show how the chameleon
mechanism weakens some of the constraints on cyclic potentials.
