  The weak charge of the proton determines its coupling to the $Z^0$ boson. The
distribution of weak charge is found to be dramatically different from the
distribution of electric charge. The proton's weak radius $R_W= 1.545\pm 0.017$
fm is 80\% larger than its charge radius $R_{ch}\approx 0.84$ fm because of a
very large pion cloud contribution. This large weak radius can be measured with
parity violating electron scattering and may provide insight into the structure
of the proton, various radiative corrections, and possible strange quark
contributions.
