  We present a model in which elementary particles and forces are unified in
the framework of quantum field theory in higher dimensions. The particles
include gauge bosons, quarks and leptons, as well as the Higgs bosons and the
forces include strong, weak, hypercharge as well as Yukawa interactions. The
model is based on a simple group SO(16) in six dimensions with N=2
supersymmetry. The gauge symmetry, as well as supersymmetry is broken to SU(4)
x SU(2)_L x SU(2)_R x U(1)^3 with N=1 supersymmetry upon compactification in
four dimension on a T^2/Z_6 orbifold.
