There is growing awareness of the importance of adequately defining the environment when conducting ecological studies. Our objective in this chapter is to present the rationale and procedures for describing soils and landscapes (sites) for such studies. We use the term site characterization to refer to the entire suite of soil biogeophysical descriptors that places a site into an environmental context. A primary goal of any environmental study is to understand a phenomenon or set of linked phenomena, whether attributes or processes. Macro- and miroclimate, soil and landscape properties influence bot6h ecosystem attributes and processes. To understand our own data or those of others, we must understand the environment in which they were collected. In addition, we are increasingly called upon to apply our research results to land management issues. Extrapolation from study sites can be either statistically rigorous or qualitative. Both understanding than extrapolation demand good site characterization.