  Gauge/gravity duality leads to a simple, analytical, and phenomenologically
compelling nonperturbative approximation to the full light-front QCD
Hamiltonian. This approach, called "Light-Front Holography", successfully
describes the spectroscopy of light-quark meson and baryons, their elastic and
transition form factors, and other hadronic properties. The bound-state
Schrodinger and Dirac equations of the soft-wall AdS/QCD model predict linear
Regge trajectories which have the same slope in orbital angular momentum L and
radial quantum number n for both mesons and baryons. Light-front holography
connects the fifth-dimensional coordinate of AdS space z to an invariant impact
separation variable zeta in 3+1 space at fixed light-front time. A key feature
is the determination of the frame-independent light-front wavefunctions of
hadrons -- the relativistic analogs of the Schrodinger wavefunctions of atomic
physics which allow one to compute form factors, transversity distributions,
spin properties of the valence quarks, jet hadronization, and other hadronic
observables. One thus obtains a one-parameter color-confining model for hadron
physics at the amplitude level. AdS/QCD also predicts the form of a
non-perturbative effective running coupling and its beta-function with an
infrared fixed point which agrees with the effective coupling extracted from
measurements of the Bjorken sum rule below 1 GeV^2. This is consistent with a
flux-tube interpretation of QCD where soft gluons are sublimated into a
color-confining potential for quarks. We discuss a number of phenomenological
hadronic properties which support this picture.
