Many engineering structures and components contain cracks or crack-like flaws and it is widely recognized that crack growth must be considered both in the design and analysis of failures. The complete solution of a crack growth problem therefore includes determination of the crack path. At present the factors controlling the path taken by a propagating crack are not completely understood. In general crack paths are difficult to predict, while in practice their development in structures is often determined by large-scale structural tests. In introductory texts on fracture mechanics it is usually assumed that the crack path is known, either from theoretical considerations, or from the results of laboratory tests. A great amount of published information on crack paths exists, but this is scattered and often incomplete. This book provides an accessible state-of-the-art survey, with major themes presented in as unified a manner as possible.