n terms of mechanical properties, every composite laminate with a different lay-up constitutes a new material whose properties must be characterized. With small changes in the fibre, matrix or interface properties, and changes in the processing procedure, the composite must be re-characterized for judicious design. In fatigue of multidirectional laminates, the 0∘ plies govern the fatigue life performance of the laminate if interpreted in terms of initial peak strain2, 3 and 4. The 0∘ ply constitutes the critical element, since it is more resistant to fatigue and has a larger strain to failure compared to off-axis unidirectional plies[5]. The 0∘ ply is therefore the first to be examined in more detail to identify the active fatigue damage mechanisms. Extensions to more general lay-ups can then be made on the basis of results from the 0∘ plies.