  Anti-de Sitter space in five dimensions provides an exact geometrical
representation of the conformal group. Remarkably, gravity in AdS$_5$ space is
holographically dual to frame-independent light-front Hamiltonian theory,
derived from the quantization of the QCD Lagrangian at fixed light-front time
$\tau = x^0+x^3$. Light-front holography also leads to a precise relation
between the bound-state amplitudes in the fifth dimension $z$ of AdS space and
the variable $\zeta$, where $\zeta^2 = b^2_\perp x(1-x)$ is the argument of the
boost-invariant light-front wavefunctions describing the internal structure of
hadrons in physical space-time. The holographic mapping of AdS space with a
specific "soft-wall" dilaton yields a confining potential $U(\zeta^2)$ for the
light-front Schr\"odinger equation for hadrons with arbitrary spin $J$.
Remarkably, $U(\zeta^2)$ has a unique form of a harmonic oscillator potential
if one requires that the chiral QCD action remains conformally invariant. One
thus obtains an effective light-front effective theory for general spin which
respects the conformal symmetry of the four-dimensional classical QCD
Lagrangian. The predictions of the LF equations of motion include a zero-mass
pion in the chiral $m_q\to 0$ limit, and linear Regge trajectories $M^2(n,L)
\propto n+L$ with the same slope in the radial quantum number $n$ and the
orbital angular momentum $L$. The light-front AdS/QCD holographic approach
gives a frame-independent representation of color-confining dynamics, Regge
spectroscopy, as well as the excitation spectra of relativistic light-quark
meson and baryon bound states in QCD in terms of a single mass parameter. We
also briefly discuss the implications of the underlying conformal template of
QCD for renormalization scale-setting, and the implications of light-front
quantization for the value of the cosmological constant.
