Quark-hadron duality: resonances and the onset of scaling

We examine the origin of Bloom-Gilman duality and the relationship between resonances and scaling in deep-inelastic scattering. A simple quantum mechanical model is used to illustrate the essential features of Bloom-Gilman duality at low momentum transfer. As an application of local duality, we discuss model-independent relations between structure functions at x ~ 1 and elastic electromagnetic form factors.