This paper describes a robotic walker, designed as an assistive device for cognitively frail elderly people. Locomotion is most often the primary form of exercise for the elderly. Devices that provide mobility assistance are critical for the health and well being of such individuals. Previous work on walkers focused primarily on safety but offered little or no assistance with navigation and obstacle avoidance, whereas our system provides navigational guidance besides providing the stability and support of a conventional walker. This capability is achieved by a suite of software for robot localization and navigation, combined with a shared-control haptic interface. The system has been tested in a retirement facility near Pittsburgh, PA, USA, where it has been found to be highly effective.