  Effects of universal extra dimensions on Standard Model observables first
arise at the one-loop level. The quantization of this class of theories is
therefore essential in order to perform predictions. A comprehensive study of
the Standard Model defined in a space-time manifold with one universal extra
dimension, compactified on the oribifold $S^1/Z_2$, is presented. The fact that
the four-dimensional Kaluza-Klein theory is subject to two types of gauge
transformations is stressed and its quantization under the basis of the BRST
symmetry discussed. A $SU_C(3) x SU_L(2) x U_Y(1)$-covariant gauge-fixing
procedure for the Kaluza-Klein excitations is introduced. The connection
between gauge and mass eigenstates fields is established in an exact way. An
exhaustive list of the explicit expressions for all physical couplings induced
by the Yang-Mills, Currents, Higgs, and Yukawa sectors is presented. The
one-loop renormalizability of the standard Green's functions, which implies
that the Standard Model observables do not depend on a cutoff scale, is
stressed.
