This chapter discuses navigation systems from a spatial database perspective. Navigation systems that guide objects moving from one place to another have progressed recently with the rapid advances in positioning, communication, and spatial data storage and processing technologies. Earlier navigation system that were limited to simple positioning devices and static paper maps, have evolved into much more sophisticated navigations systems, comprising satellite-based precise positioning system enabled portable digital assistants. These devices have local memories to support small digital maps and have wireless communication ports for getting dynamic spatial information from remote back-end spatial database (SDB) servers. Spatial database systems serve various spatial data (e.g., digital road maps) and nonspatial information on request to the client. SDB servers provide efficient geospatial query-processing capabilities, such as find the nearest neighbor to a given location and find the shortest path to the destination. The SDB system acts as a back-end server to the GeoMobility server. Thus, SDB servers play a crucial role in implementing efficient and sophisticated navigation system applications.