  A quantitative understanding of isospin violation is an increasingly
important ingredient for the extraction of the nucleon's strange vector form
factors from experimental data. We calculate the isospin violating electric and
magnetic form factors in chiral perturbation theory to leading and
next-to-leading order respectively, and we extract the low-energy constants
from resonance saturation. Uncertainties are dominated largely by limitations
in the current knowledge of some vector meson couplings. The resulting bounds
on isospin violation are sufficiently precise to be of value to on-going
experimental studies of the strange form factors.
