  Chameleon and similar (symmetron and dilation) theories of gravity can
exhibit new and interesting features on cosmological scales whilst screening
the modifications on small scales thereby satisfying solar system tests of
general relativity. This thesis explores the regime between these two scales:
astrophysics. The majority of this thesis is focused on discerning new and
novel astrophysical probes of chameleon gravity in the form of stellar
structure and oscillation tests. These are used to place new constraints on the
theory parameters and the implications of these are discussed, as are the
future prospects for improving them using planned future surveys. The final two
chapters review supersymmetric completions of these theories.
