We discuss single transverse spin asymmetries in the Drell-Yan process
originating from so-called gluonic poles in twist-three hadronic matrix
elements, as first considered by Qiu and Sterman. Even though time-reversal
invariance is not broken, the effects of such poles cannot be distinguished
from those of time-reversal odd distribution functions. We show the connection
between gluonic poles and large distance gluon fields, in particular we focus
on boundary conditions. We identify the possible single spin asymmetries in the
Drell-Yan process.Comment: 10 pages, Latex, 4 Postscript figure, uses epsfig.sty. Invited talk
presented at the workshop 'Deep inelastic scattering off polarized targets:
theory meets experiment', DESY-Zeuthen, September 1-5, 199