Abstract: The use of polymeric materials is widespread in virtually every application within our society today.  They are now commonplace engineering materials of choice in many applications including, automotive, aerospace, housing, and medical applications.  This is due in large part to the multitude of synthetic routes, molecular architectures, and processing strategies that enable an infinite range of materials with unique properties.  In this lecture, we discuss aspects that relate molecular architecture and segmental mobility to engineering performance.   We start by highlighting how basic alterations in molecular architecture affect key thermal and mechanical properties of glassy networks.  We then discuss how these characteristics relate to nonlinear properties including the yield behavior, the post yield response, and fracture behavior.  We illustrate how these properties change during the formation of the glass and how they are altered by process or cure conditions.  We then present results that probe segmental mobility during active nonlinear deformation in a model glass.  We distinguish between flow in a polymer melt to that of vitreous flow observed in polymer glass subjected to large inelastic deformation.