The advent of high-precision antihydrogen spectroscopy has opened up the
possibility of direct tests with unprecedented accuracy of some of the
most fundamental principles of physics, notably Lorentz and CPT symmetry
and the Einstein equivalence principle.
This book reviews these principles, emphasising their interconnections
in quantum field theory and general relativity and the special role of
antimatter, and explores how they may be tested in current and
forthcoming experiments on antihydrogen. Original research results
relevant to the experimental programme of the ALPHA collaboration at
CERN are presented, together with the implications for antihydrogen of
proposed theories featuring novel `fifth-force' interactions.