A mobile robot navigating to a goal will encounter obstacles that must be avoided. Obstacle avoidance is presented in the context of wall following: moving around the wall of the obstacle until it no longer prevents access to the goal. Three algorithms are presented: simple wall following which fails in the presence of multiple obstacles, wall following with direction that also fails for certain obstacles and the Pledge algorithm which can avoid these obstacles. To demonstrate finding a path to a goal, an algorithm is presented that is based upon the behavior of a colony of ants searching for a food source even though they do not know its location. A probabilistic model explains the success of the algorithm.