During the late 1960s and early 1970s, an enthusiastic group of researchers at the SRI AI Laboratory focused their energies on a single experimental project in which a mobile robot was being developed that could navigate and push objects around in a multi-room environment (Nilsson [11]) . The project team consisted of many people over the years, including Steve Coles, Richard Duda, Richard Fikes, Tom Garvey, Cordell Green, Peter Hart, John Munson, Nils Nilsson, Bert Raphael, Charlie Rosen, and Earl Sacerdoti. The hardware consisted of a mobile cart, about the size of a small refrigerator, with touch-sensitive feelers, a television camera, and an optical range-finder. The cart was capable of rolling around an environment consisting of large boxes in rooms separated by walls and doorways; it could push the boxes from one place to another in its world. Its suite of programs consisted of those needed for visual scene analysis (it could recognize boxes, doorways, and room corners), for planning (it could plan sequences of actions to achieve goals), and for converting its plans into intermediatelevel and low-level actions in its world. When the robot moved, its television camera shook so much that it became affectionately known as Shakey the Robot. The robot, the environment, and the tasks performed by the system were quite simple by today's standards, but they were sufficiently paradigmatic to enable initial explorations of many core issues in the development of intelligent autonomous systems. In particular, they provided the context and motivation for development of the A* search algorithm (Hart et al. [7] ), the STRIPS (Fikes and Nilsson [4] ) and ABSTRIPS (Sacerdoti [ 14] ) planning systems, programs for generalizing and learning macro-operators