Midlatitude cyclonic cloud systems are common occurrences that significantly impact our climate. In this review, attention is paid to those physical characteristics of these cloud systems with large-scale impacts that must be accounted for in climate simulations. Such attributes include atmospheric forcing, internal structure, surface influences, cloud layering, microphysics, precipitation, water cycling, and radiation. Because of their present limitations associated with, for example, grid sizes and simplified parameterizations, climate models cannot account for all the crucial impacts of these cloud systems. Future advances in the representation of these systems within climate models will need to rely in part on rigorous assessments of model capabilities in a variety of conditions. ¿ 1998 American Geophysical Union