The potential benefits of including geophysical data in hydrogeological site characterization have been stated numerous times (e.g. Ezzedine et al., 1999; Hubbard et al., 1999; Chen et al., 2001; Hubbard and Rubin, 2005). The principle reason for the growing interest in using geophysical methods in hydrogeological studies is that geophysics may provide spatially distributed models of physical properties in regions that are difficult to sample using conventional hydrological wellbore methods (e.g. Butler, 2005). The geophysical models often reveal more details compared with hydrogeological models derived from hydrogeological data, such as pump tests and observations of hydraulic heads. Furthermore, geophysical methods are less invasive compared with hydrogeological methods and they are comparatively cheap. Therefore, geophysical surveys can improve hydrogeological characterization if we could relate the geophysical and hydrogeological properties in an appropriate way. The added value of including geophysics in hydrogeological characterization has become increasingly accepted and several published case studies clearly show the worth of including geophysics for different applications and data types (e.g. see reviews by Hyndman and Tronicke, 2005; Goldman et al., 2005; Daniels et al., 2005). However, the success of a given hydrogeophysical case-study is dependent on many different factors and it is often difficult to develop an opinion a priori about the applicability of a method at another site or for another application. Here, we discuss some of the choices that need to be considered in a characterization effort and point out similarities and fundamental differences between different hydrogeophysical parameter estimation approaches presented in the literature.