  Gravitational-wave sources offer us unique testbeds for probing strong-field,
dynamical and nonlinear aspects of gravity. In this chapter, we give a brief
overview of the current status and future prospects of testing General
Relativity with gravitational waves. In particular, we focus on three
theory-agnostic tests (parameterized tests, inspiral-merger-ringdown
consistency tests, and gravitational-wave propagation tests) and explain how
one can apply such tests to example modified theories of gravity. We conclude
by giving some open questions that need to be resolved to carry out more
accurate tests of gravity with gravitational waves.
