William J. Likos, Ph.D., M.ASCE, is an Associate Professor in the Department of Civil and Environmental Engineering at the University of Missouri. His primary research interests center on experimental and numerical methods for understanding the mechanical and hydrologic behavior of unsaturated soils for geotechnical and geoenvironmental engineering applications. This includes investigations of fluid flow and contaminant transport in near-surface evapotranspirative waste barrier systems, swelling behavior of expansive clay minerals, and effective stress concepts for unsaturated soils. Major projects have been funded by the National Science Foundation, the American Chemical Society, the Integrated Ocean Drilling Program, and the Missouri Department of Transportation. Professor Likos is author of more than 40 refereed technical publications and co-author of Unsaturated Soil Mechanics. He is recipient of the 2007 ASCE Norman Medal and the 2005 Arthur Casagrande Award. He currently serves as co-editor of the American Society for Testing and Materials (ASTM) Geotechnical Testing Journal, an editorial board member for the ASCE Journal of Geotechnical and Geoenvironmental Engineering, the journal Applied Clay Science, and as Chair of committee A2L06, committee on Engineering Behaviour of Unsaturated Soils, for the Transportation Research Board.