  We discuss the links between Generalized Parton Distributions (GPDs) and
elastic nucleon form factors. These links, in the form of sum rules, represent
powerful constraints on parametrizations of GPDs. A Regge parametrization for
GPDs at small momentum transfer, is extended to the large momentum transfer
region and it is found to describe the basic features of proton and neutron
electromagnetic form factor data. This parametrization is used to estimate the
quark contribution to the nucleon spin.
