This book deals with the experimental investigation of the delamination under mode I fatigue. The objective of this research is the development of a mechanistic model for delamination growth that is based on the observed delamination mechanisms and the effects of monotonic and cyclic loadings in fatigue. Based upon fractographic evidence, a two-parameter model has been developed in which the contribution of monotonic and cyclic loading are superimposed rather than multiplied. The model has been validated with experiments and various data from the literature.