This study reviews processes for developing and evaluating conceptual models of fluid flow and solute transport in the unsaturated zone between the land surface and the water table. The panel report provides guidance to regulatory agencies for site licensing, and identifies areas for future research. Additionally, ten papers summarize recent research on such topics as models for weathered shales, uniform and preferential flow mechanisms, free-surface films, surface wetting and network geometry effects on fracture flow, and environmental traces. No index. Annotation c. Book News, Inc., Portland, OR (booknews.com)