The International Symposium on Rules, Applications and Interoperability has evolved from an annual series of international workshops since 2002, international conferences in 2005 and 2006, and international symposia since 2007. This year, the 3rd International Symposium on Rules, Applications and Interoperability (RuleML-2009) takes place in Las Vegas, Nevada, USA. RuleML-2009 is devoted to practical distributed rule technologies and rule-based applications which need language standards for rules (inter)operating in, e.g., the Semantic Web, Multi-Agent Systems, Event-Driven Architectures, and Service-Oriented Applications.