A stretchable conductor is the most fundamental component of a stretchable circuit. Nanocomposites involving conductive nanomaterials have been widely used as stretchable conductors; metal nanowires ( NWs ) are one of the most promising conductive nanomaterials for this purpose. In this chapter, we review the mechanics issues of metal NWs of relevance to their application in stretchable electronics, including mechanics of individual NWs, interfacial mechanics between NWs and polymer matrix, and mechanics of NW/polymer composite in stretchable structures. Metal NWs with internal structures like twin boundaries possess excellent mechanical properties such as recoverable plasticity, strain hardening, large ductility, and insensitivity to surface flaws. The NW–polymer interfacial interactions typically include van der Waals interactions and chemical bonding. The interactions determine the interfacial shear stress transfer, which imparts the strain in the polymer matrix to the NWs. Mechanical design has been applied to the NW/polymer nanocomposites to develop highly stretchable structures. Fracture behavior of NW/polymer composite is discussed, including crack propagation, opening, and blunting, for the development of a highly stretchable, sensitive, and robust strain sensor. The mechanics issues discussed here can be applied to other nanomaterials in the form of nanocomposites used in stretchable electronics.