This review discusses multiscale modeling and simulations of macromolecules and macromolecular systems in the context of two specific examples. In the first, recent attempts to develop coarse-grained representations of DNA are reviewed, and a discussion of recent predictions of such models is presented, particularly in the context of DNA melting and rehybridization. The second example considers polymer nanocomposites; a review of recent simulations is presented, with an emphasis on the description of entanglements in such systems and new methods for the study of the segregation of nanoparticles that arises in copolymers, in which composition heterogeneity can be used to control nanoparticle position and develop an increased understanding of nanoparticle-polymer interactions.