These proceedings contain the papers accepted for presentation at the Second International Semantic Web Conference (ISWC 2003) held on Sanibel Island, Florida, U. S. A. , October 20–23, 2003. Following the success of ISWC 2002 that washeldinSardiniainJune2002,ISWC2003enjoyedagreatlyincreasedinterest in the conference themes. The number of submitted papers more than doubled compared with ISWC 2002 to 283. Of those, 262 were submitted to the research track and 21 to the industrial track. With rare exceptions, each submission was evaluated by three program committee members whose reviews were coordinated by members of the senior program committee. This year 49 papers in the research track and 9 papers in the industrial track were accepted. The high quality of ISWC 2003 was the result of the joint e?ort of many people. First of all we would like to thank the authors for their high-quality submissions and the members of the program committee for their reviewing and review coordination e?orts. We would like to extend special thanks to Christoph Bussler for chairing the industrial track, to Mike Dean for his help with the conference management software, the web site, and conference publicity, and to Massimo Paolucci for helping with the organization of the proceedings and arranging sponsorships.