What is a 3D Geographical Information system (GIS)? Why is this technology so diverse from all the other data management systems? What can we achieve with this tool and how is its implementation in the field impacting archaeological practice? This chapter explores the role of 3D GIS in the frame of archaeological field practice and provides an overview of how this technology has been used for answering various research questions. In the first part of the chapter, we discuss emerging interest in 3D data in archaeology, and remark on the importance of how these changes impact our practice and affect the process of knowledge production. The second part of the chapter describes one of the first experiments carried out by the authors in which 3D GIS was used for supporting research carried out in the Swedish Pompeii Project. The chapter contains a few informative BOXes which illustrate the methodology initially developed for implementing 3D boundary models in the 3D GIS. This approach is still useful today when dealing with datasets which lack spatial reference (such as ground control points), and it can also be used for reusing and contextualising datasets from records that are no longer available in the physical world.