  We identify an invariant light-front coordinate $\zeta$ which allows the
separation of the dynamics of quark and gluon binding from the kinematics of
constituent spin and internal orbital angular momentum. The result is a
single-variable light-front Schrodinger equation for QCD which determines the
eigenspectrum and the light-front wavefunctions of hadrons for general spin and
orbital angular momentum. This frame-independent light-front wave equation is
equivalent to the equations of motion which describe the propagation of
spin-$J$ modes on anti-de Sitter (AdS) space. Light-front holography is a
remarkable feature of AdS/CFT: it allows hadronic amplitudes in the AdS fifth
dimension to be mapped to frame-independent light-front wavefunctions of
hadrons in physical space-time, thus providing a relativistic description of
hadrons at the amplitude level. In principle, the model can be systematically
improved by diagonalizing the full QCD light-front Hamiltonian on the AdS/QCD
basis. Quark and gluon hadronization can be computed at the amplitude level by
convoluting the off-shell $T$ matrix calculated from the QCD light-front
Hamiltonian with the hadronic light-front wavefunctions. We also note the
distinction between static observables such as the probability distributions
computed from the square of the light-front wavefunctions versus dynamical
observables such as the structure functions and the leading-twist single-spin
asymmetries measured in deep inelastic scattering which include the effects of
initial and final-state interactions.
