Delamination crack growth in a unidirectional composite laminate under static and fatigue loading conditions is investigated. An experimental program was performed to elucidate failure mechanisms and to characterize the growth rate of the delamination crack. Analytical modeling, based on microscopic observation, is conducted by using an advanced singular finite element method of the hybrid-stress model formulated through the minimum complementary energy principle. Solutions obtained from the analysis probe the fundamental nature of the problem. Implications of the results on the applicability of the classical laminate theory are discussed. Using a mixed-mode failure criterion, the delamination growth under a monotonically increasing load may be predicted satisfactorily. The rate of delamination crack propagation under fatigue loading is found to be related directly to the amplitudes of cyclic opening and shearing mode stress intensity factors by a power law relationship. The study elucidates many salient features of the problem, provides insight to the basic nature of the delamination failure behavior, and should be of practical importance in the design and testing of composite materials.