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A fatigue crack normally grows in so-called mode I, with a flat fracturesurface perpendicular to the loading direction. This can also be directed as squarecrack growth. Sometimes the crack front becomes slanted, at about 45° with the loadingdirection. In that case it is possible that the original crack growth direction ismaintained, but also a deviated growth direction can be found. The paper describesvarious effects related to the occurrence of slant growth due to shear lips on fatiguefracture surfaces in (thin) sheets. After a general introduction the attention is focusedon the relations between shear lips and fatigue crack growth. Questions about whyshear lips develop and about other aspects of shear lip behavior will be answered.Several interaction effects combining shear lip behavior and fatigue crack growth rateare summarized, including the effects of frequency and environment.