Polarized parton distribution functions

Polarized parton distribution functions for a hadron target are defined in terms of gauge-invariant correlation functions. The polarized gluon contribution to the ${\mathit{g}}_1$ structure function of the nucleon is computed using the modified minimal-subtraction scheme as a simple example of the calculational method. The gluon contribution to the integral of the ${\mathit{g}}_1$ structure function is shown to vanish.