  This talk presents issues pertaining to the quark structure of the pion
within QCD, both from the theoretical and from the experimental point of view.
We review and discuss the pion-photon transition form factor and the pion's
electromagnetic form factor vs. corresponding experimental data from the CLEO
Collaboration and the JLab. We also examine the extent to which recent
high-precision lattice computations of the second moment of the pion's
distribution amplitude conform with theoretical models. Finally, we include
predictions for the azimuthal asymmetry of the $\mu^+$ distribution in the
polarized $\mu$-pair-induced DY production employing various pion distribution
amplitudes.
