The behavior of a robot is reactive if values returned by the sensors directly affect the actuators. Two families of reactive behavior are presented. Braitenberg vehicles are very simple robots that demonstrate relatively complex behavior. A robot with ground sensors can follow a line on a surface and thus navigate a known environment such as a warehouse. Three algorithms are presented: an algorithm that uses two ground sensors, an algorithm that uses only one ground sensor on a line with a gradient and an algorithm that follows the edge of a line.