The research project "AN.ON - Anonymity online" focuses on developing and providing a web anonymising service. This service provides anonymity and unobservability against external observers, the user?s ISP and the operators of the service themselves. AN.ON is being promoted by the German Federal Ministry of Economic Affairs for three years (2001-2003). Main criteria for the design of the web anonymising service are security, trustworthiness, performance and usability. Of utmost importance is legal compliance, especially with respect to data protection law. In the submitted paper the project partners, Dresden University of Technology resp. Freie Universit?t Berlin and Independent Centre for Privacy Protection Schleswig-Holstein, Germany, describe technical background, legal topics, economic issues, socio-political side effects and practical experiences in developing and operating this web anonymising service.