  We discuss strategies to determine hadronic decay couplings from lattice
studies. As an application, we explore the decay of a vector meson to two
pseudoscalar mesons with $N_f=2$ flavours of sea quark. Although we are working
with quark masses that do not allow a physical decay, we show how the
transition rate can be evaluated from the amplitude for $\rho \to \pi \pi$ and
from the annihilation component of $\pi \pi \to \pi \pi$. We explore the decay
amplitude for two different pion momenta and find consistent results. The
coupling strength we find is in agreement with experiment. We also find
evidence for a shift in the $\rho$ mass caused by mixing with two pion states.
