  We present a theroretical treatment of electric dipole (E1) transitions of
heavy quarkonia based on effective field theories. Within the framework of
potential nonrelativistic QCD (pNRQCD) we derive the complete set of
relativistic corrections at relative order $v^2$ to the decay rate in a
systematic, model-independent way. Former results from potential model
calculations will be scrutinized and a phenomenological analysis with lattice
input in relation to experimental data will be presented.
