Potential fields is popular technique in autonomous robotics. The Electric Field Approach is such a technique used for high level robot control. The approach was developed by Team Sweden for use in RoboCup 2000, a soccer competition for mobile robots. This thesis describes several improvements that has been made while preparing for RoboCup 2001. The improvements are used to create simple behaviors which achieve a form of implicit cooperation and also more active defence. This thesis also describes improvement ideas that failed to show the de-sired improvement and the reason for this is discussed, thereby deepening the understanding of the Electric Field Approach.