Hydrogeophysics was conceived as a vehicle for disseminating some of the background and current research presented at a NATO funded Hydrogeophysics Advanced Study Institute, which was held in the Czech Republic in 2002. We thank Philippe Baveye for initiating the development of this Institute, NATO for funding the Institute, and Miroslav Kobr for serving as a wonderful host for our meeting. Thirty five authors from nine countries, who are leaders in their respective areas, contributed to Hydrogeophysics. We are grateful to this outstanding author group for their efforts in developing their chapters and for reviewing other chapters. We also thank the external reviewer group, including: Alex Becker, Niels Christianson, Tom Daley, Sander Huisman, Rosemary Knight, Zbigniew Kabala, Niklas Linde, Seiji Nakagawa, Peter Styles, and Vitaly Zlotnik. We particularly thank Lee Slater for reviewing several chapters within demanding timeframes.