  We study the three-quark light-cone amplitudes of the proton including
quarks' transverse momenta. We classify these amplitudes using a
newly-developed method in which light-cone wave functions are constructed from
a class of light-cone matrix elements. We derive the constraints on the
amplitudes from parity and time-reversal symmetries. We use the amplitudes to
calculate the physical observables which vanish when the quark orbital angular
momentum is absent. These include transverse-momentum dependent parton
distributions $\Delta q_T(x, k_\perp)$, $q_T(x, k_\perp)$, $\delta q(x,
k_\perp)$, and $\delta q_L(x,k_\perp)$, twist-three parton distributions
$g_T(x)$ and $h_L(x)$, helicity-flip generalized parton distributions $E(x,
\xi=0, Q^2)$ and its associates, and the Pauli form factor $F_2(Q^2)$.
