Small structures of the micro/nanometer scale, such as electronic/optic devices and MEMS/NEMS have been developed, and the size of their elements now approaches the nano/atomic scale. This book discuses the fracture behavior of nano/atomic elements (nanofilms, nanowires, and so on) and focuses on the initiation and propagation of interface crack and mechanical instability criterion of atomic structures. This covers the fundamentals and the applicability of the top-down (conventional fracture mechanics to nanoscale) and bottom-up (atomic mechanics including ab initio simulation) concepts. New areas, such as multiphysics characteristics of nanoelements, are introduced as well.