Autonomous mobile robots are ever increasing their number of different applications; even in ludic application or in sports. In the last few years; several competitions of football have been organised with lots of teams participating. This paper describes an Autonomous Mobile Robot which plays football and it was developed at the Industrial Electronics Engineering department of the University of Minho in Guimar√£es; Portugal. Each team is free to solve on his own way all the different electronics; sensory systems; playing algorithms; etc. as far as they cope with the rules imposed by the organisation. Instead of using several different sensors increasing electronics complexity; it was decided to use only one major sensor namely a vision system with the use of a colour camera. All the image processing algorithms were developed from scratch and are hereby described. This vision system uses an innovative approach. In order to see the whole field; a convex mirror was placed on the top of the robot looking downwards with the video camera looking upwards towards the mirror. This way; the robot can see both goals; the ball and other robots; almost all the time; as well as having a top view.