The mechanics of interface cracks has recently been clarified (e.g., [1]) and a number of efforts are underway to develop a mechanics of interface fracture with applications to composite materials, thin film/substrate systems, and coatings. An intrinsic feature of interfacial fracture is its mixed mode character wherein both shear and normal stresses act on the interface directly ahead of the crack. Depending on geometry and loading, the mixture of modes can range from purely normal stresses (mode I) to purely shear stresses (mode II). Toughness of an interface is characterized by critical combinations of mode I and mode II stress intensity factors (i.e., a locus of critical combinations) rather than just the single critical mode I stress intensity factor in the fracture of homogeneous materials. Equivalently, the critical energy release rate depends on the mode combination for interfacial fracture. Solutions are now available to the following problems: an interface crack in a layered structure where a very thin layer is sandwiched between two thick layers of different material [2], an interface crack between two layers of arbitrary thickness subject to arbitrary combinations of bending and stretching loads [3], and a crack in a substrate paralleling an interface between a thin film and the substrate driven by a variety of loadings including residual tension in the film [4]. These solutions can be used to analyze specimens for determining interfacial toughness and for predicting cracking in thin film or layered structures.