Theoretical and experimental studies of the effects of contacting asperities on the scattering of elastic waves from fatigue cracks are reported. The analysis is based on a generalization of the representation integral for scattering from a crack to a form explicitly including the transducer radiation patterns. A series of approximations are developed based on various models for the form of the dynamic crack-opening displacement (COD) which appears within the integral. The theory is compared to experimental scattering measurements for fatigue cracks grown in aluminum compact tension specimens. These show that a simple quasistatic model for the COD is adequate to describe measurements of transmission through the crack, but that the discreteness of the contacts must be included if the signals diffracted from the crack tip are to be predicted accurately. Applications of the results to characterize the closure state and the resulting changes in the growth rate of fatigue cracks is presented. This latter point is supported by a discussion of the relationship between the contact parameters and crack tip shielding at the lower loads of the fatigue cycle.