  We present a class of N=1 supersymmetric ``standard'' models of particle
physics, derived directly from heterotic M-theory, that contain three families
of chiral quarks and leptons coupled to the gauge group SU(3)_C X SU(2)_L X
U(1)_Y. These models are a fundamental form of ``brane world'' theories, with
an observable and hidden sector each confined, after compactification on a
Calabi--Yau threefold, to a BPS three-brane separated by a higher dimensional
bulk space with size of the order of the intermediate scale. The requirement of
three families, coupled to the fundamental conditions of anomaly freedom and
supersymmetry, constrains these models to contain additional five-branes
located in the bulk space and wrapped around holomorphic curves in the
Calabi--Yau threefold.
