Central assertions in setting up the parton model for DIS (Sec. 2.4) were that hard scattering occurs off a single parton constituent of the target, and that the hard scattering is just the Born approximation for electron-quark scattering. In fact, both assertions fail if taken literally. So in this chapter I show how to derive correct statements about the dominant configurations in DIS and the many other cases of interest. I will interleave a general treatment with a detailed discussion of specific examples.