Tests of Chameleon Gravity
  Theories of modified gravity where light scalars with non-trivial
self-interactions and non-minimal couplings to matter-chameleon and symmetron
theories-dynamically suppress deviations from general relativity in the solar
system. On other scales, the environmental nature of the screening means that
such scalars may be relevant. The highly-nonlinear nature of screening
mechanisms means that they evade classical fifth-force searches, and there has
been an intense effort towards designing new and novel tests to probe them,
both in the laboratory and using astrophysical objects, and by reinterpreting
existing datasets. The results of these searches are often presented using
different parametrizations, which can make it difficult to compare constraints
coming from different probes. The purpose of this review is to summarize the
present state-of-the-art searches for screened scalars coupled to matter, and
to translate the current bounds into a single parametrization to survey the
state of the models. Presently, commonly studied chameleon models are
well-constrained but less commonly studied models have large regions of
parameter space that are still viable. Symmetron models are constrained well by
astrophysical and laboratory tests, but there is a desert separating the two
scales where the model is unconstrained. The coupling of chameleons to photons
is tightly constrained but the symmetron coupling has yet to be explored. We
also summarize the current bounds on $f(R)$ models that exhibit the chameleon
mechanism (Hu \& Sawicki models). The simplest of these are well constrained by
astrophysical probes, but there are currently few reported bounds for theories
with higher powers of $R$. The review ends by discussing the future prospects
for constraining screened modified gravity models further using upcoming and
planned experiments.
