Abstract: The authors are collecting data on the methods, scope, and depth of selective barriers to Internet access through Chinese networks. Tests from May 2002 through November 2002 indicate at least four distinct and independently operable methods of Internet filtering, with a documentable leap in filtering sophistication beginning in September 2002. The authors document thousands of sites rendered inaccessible using the most common and longstanding filtering practice. These sites were found through connections to the Internet by telephone dial-up link and through proxy servers in China. Once so connected, the authors attempted to access approximately two hundred thousand web sites. The authors tracked 19,032 web sites that were inaccessible from China on multiple occasions while remaining accessible from the United States. Such sites contained information about news, politics, health, commerce, and entertainment. The authors conclude (1) that the Chinese government maintains an active interest in preventing users from viewing certain web content, both sexually explicit and non-sexually explicit; (2) that it has managed to configure overlapping nationwide systems to effectively - if at times irregularly - block such content from users who do not regularly seek to circumvent such blocking; and (3) that such blocking systems are becoming more refined even as they are likely more labor- and technology-intensive to maintain than cruder predecessors.