  We have recently proposed an alternative picture for the physics at the scale
of gauge coupling unification, where the unified symmetry is realized in higher
dimensions but is broken locally by a symmetry breaking defect. Gauge coupling
unification, the quantum numbers of quarks and leptons and the longevity of the
proton arise as phenomena of the symmetrical bulk, while the lightness of the
Higgs doublets and the masses of the light quarks and leptons probe the
symmetry breaking defect. Moreover, the framework is extremely predictive if
the effective higher dimensional theory is valid over a large energy interval
up to the scale of strong coupling. Precise agreement with experiments is
obtained in the simplest theory --- SU(5) in five dimensions with two Higgs
multiplets propagating in the bulk. The weak mixing angle is predicted to be
sin^2theta_w = 0.2313 \pm 0.0004, which fits the data with extraordinary
accuracy. The compactification scale and the strong coupling scale are
determined to be M_c \simeq 5 x 10^{14} GeV and M_s \simeq 1 x 10^{17} GeV,
respectively. Proton decay with a lifetime of order 10^{34} years is expected
with a variety of final states such as e^+pi^0, and several aspects of flavor,
including large neutrino mixing angles, are understood by the geometrical
locations of the matter fields. When combined with a particular supersymmetry
breaking mechanism, the theory predicts large lepton flavor violating mu -> e
and tau -> mu transitions, with all superpartner masses determined by only two
free parameters. The predicted value of the bottom quark mass from Yukawa
unification agrees well with the data. This paper is mainly a review of the
work presented in hep-ph/0103125, hep-ph/0111068 and hep-ph/0205067.
