NAVIGATOR addresses issues of robot navigation in partially unknown environments. It employs landmarks as well as spatial relationships between them for space perception and localization purposes. The system"s knowledge of the environment is specified from the contents of a visual memory, which contains a large number of patterns corresponding to landmark descriptions known to the system. The visual recognition of landmarks, using a set of qualitative descriptors, in conjunction with the visual memory, facilitates navigation without the need of environment maps and beacons, used in traditional approaches.