The macroscopic theory of polymer deformation and the use of NMR for the study of polymeric materials under tension are discussed. Some examples are presented that are typical enough to show the possibilities and impossibilities of NMR for such investigations. It is clear that the combination of stretching devices with NMR spectrometers severely limits the type of NMR expts. that can be explored. Nevertheless, enough possibilities remain to study polymers under stress with NMR, as shown for instance by the study of polymer networks.