Geographical information systems (GIS) are the systems that store location-based data and analyze them. GIS originated from the conventional cartographic techniques of simply drawing maps with a pencil and board. Following the adoption of computer technology, GIS further evolved as a geo-referenced dynamic information system, which can today be considered as a multi-disciplinary instrument that links different disciplines like geography, computer science, remote sensing, civil engineering, statistics, marketing, and other social and behavioral sciences. In this chapter, GIS is defined and its importance and functions are described in detail. Usage of GIS in marketing is explained, especially its development in marketing theory. Also, the value and scope of GIS in tourism management with a view to understand the spread of GIS applications in tourism is explored.