US domestic extremist groups have increased in number and are intensively utilizing the Internet as an effective tool to share resources and members with limited regard for geographic, legal, or other obstacles. Researchers find that monitoring extremist and hate groups’ web sites and analyzing their usage and content have become time consuming and challenging. In response, this chapter describes the development of automated or semiautomated methodologies for capturing, classifying, and organizing domestic extremist web site data and using them for analysis. We found that by analyzing the hyperlink structures and content of domestic extremist web sites and constructing social network maps, their interorganizational structure and cluster affinities could be identified. Such analysis results could help experts in terrorism, law enforcement, intelligence, and policy making domains better understand the domestic extremist phenomena and eventually boost our national security.