  In the gauge theory context, a definition of branching ratios and partial
widths of unstable particles is proposed that satisfies the basic principles of
additivity and gauge independence. A simpler definition, similar to the
conventional one, is examined in the Z^0-boson case. In order to establish
contact with experiment, we show that it leads to a peak cross section that
justifies the expression used by the LEP Electroweak Working Group through
next-to-next-to-leading order, provided that the pole rather than the on-shell
mass and width of the Z^0 boson are employed.
