The task of characterizing optical wave propagation through the earth's atmosphere under low-visibility weather conditions is extremely difficult; it requires, in essence, solution of the general multiple-scattering problem. This paper describes results from an integrated approach to propagation through the turbid atmosphere in which experiments are used to establish the magnitude of the propagation effects and to supply empirical relationships which permit simplifying approximations in the theory. In particular, line-of-sight laser measurements of multipath spread, angular spread, beam spread, and incoherent source measurements of angular spread and power transmission versus range are reported. From the behavior of these data two approximate propagation theories, viz., multiple forward scatter and strong multiple scatter, are developed.