Spatial methods that build upon Geographic Information Systems are spreading quickly across the social sciences. This essay points out that the appropriate use of spatial tools requires more careful thinking about spatial concepts. As easy as it is now to measure distance, it is increasingly important to understand what we think it represents. To interpret spatial patterns, we need spatial theories. We review here a number of key concepts as well as some of the methodological approaches that are now at the disposal of researchers, and illustrate them with studies that reflect the very wide range of problems that use these tools.