  We use QCD sum rules to obtain the weak parity-violating pion-nucleon
coupling constant $f_{\pi NN}$. We find that $f_{\pi NN}\approx 2\times
10^{-8}$, about an order of magnitude smaller than the ``best estimates'' based
on quark models. This result follows from the cancellation between perturbative
and nonperturbative QCD processes not found in quark models, but explicit in
the QCD sum rule method. Our result is consistent with the experimental upper
limit found from $^{18}$F parity-violating measurements.

Nuclear Theory