  The quark orbital angular momentum component of proton spin, $L_q$, can be
defined in QCD as the integral of a Wigner phase space distribution weighting
the cross product of the quark's transverse position and momentum. It can also
be independently defined from the operator product expansion for the
off-forward Compton amplitude in terms of a twist-three generalized parton
distribution. We provide an explicit link between the two definitions,
connecting them through their dependence on partonic intrinsic transverse
momentum. Connecting the definitions provides the key for correlating direct
experimental determinations of $L_q$, and evaluations through Lattice QCD
calculations. The direct observation of quark orbital angular momentum does not
require transverse spin polarization, but can occur using longitudinally
polarized targets.
