The career of Karl Weissenberg began with X-ray structure studies of biopolymers. His background in scattering theory clearly affected his later approach to the measurements and modelling of the rheology of complex fluids. We show how the combination of scattering and rheology now informs molecular theories of the flow of entangled polymer melts. Very recently, the concepts generated by linear rheology have themselves contributed to the study of dynamics in biopolymers via single molecule experiments.