The statistical description of acoustic propagation is often formulated to second order using the space-time covariance of the pressure fluctuations. However, in many cases a greater insight is obtained if the second-order statistics are given in the form of the mutual coherence function and its normalized version, the complex degree of coherence. The principal advantage in this approach is that it allows the second-order statistics to be separated into amplitude and phase components. This separation enables a useful characterization of the statistical properties of a multisensor system to be made and, in particular, it leads to a direct relationship between the performance of that system and the coherence properties of the medium. In this paper these concepts are discussed and are illus-strated with the results from a long-range propagation experiment.