  Parity violation in the gravitational interaction has an important impact on
fundamental observables and the evolution of the universe. We here investigate
for the first time our ability to probe the parity violating nature of the
gravitational interaction using gravitational waves from spin-precessing
binaries. Focusing on dynamical Chern-Simons gravity, we derive the
spin-precession equations, calculate the gravitational waves emitted by
spin-precessing, quasi-circular black hole binaries and estimate the level to
which the theory could be constrained with future gravitational wave
observations.
