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As is well known many engineering structures and components, madefrom metallic materials, contain cracks or crack-like flaws. It is widely recognised thatfatigue crack growth must be considered both in design and in the analysis of failures.The complete solution of a fatigue crack growth problem includes determination of thecrack path. Macroscopic aspects of fatigue crack paths have been of industrial interestfor a very long time. At the present state of the art the factors controlling the path takenby a growing fatigue crack are not completely understood. In the last four decades therehave been substantial advances in the understanding and prediction of fatigue crackpaths, largely through developments in fracture mechanics and in the application ofmodern computers and microscopes. The purpose of this introductory paper is to set thescene for the more detailed papers which follow. To do this some of the more importantideas are presented and illustrated by examples. These have been chosen to illustratesome of the more important aspects of fatigue crack paths in metals.