  We discuss in detail a method to study transverse momentum dependent parton
distribution functions (TMDs) using lattice QCD. To develop the formalism and
to obtain first numerical results, we directly implement a bi-local quark-quark
operator connected by a straight Wilson line, allowing us to study T-even,
"process-independent" TMDs. Beyond results for x-integrated TMDs and quark
densities, we present a study of correlations in x and transverse momentum. Our
calculations are based on domain wall valence quark propagators by the LHP
collaboration calculated on top of gauge configurations provided by MILC with
2+1 flavors of asqtad-improved staggered sea quarks.
