This chapter reviews recent research on eco-terrorism and distinguishes it from radical environmental terrorism. It begins with a brief review of the history of radical environmental groups and animal rights promoters identified by the U.S. Federal Bureau of Investigation (FBI). The development of these radical environmental groups also represents the development of eco-terrorism in modern society. Eco-terrorists generally intend to attack properties or facilities but not injure humans for their specific environmental or animal right protection purposes. These eco-terrorist attacks have caused great economic loss to U.S. businesses starting in the 1990s, leading Congress to pass several federal laws to protect interests and profits of private entities, including the Animal Enterprise Protection Act of 1992 (AEPA of 1992) and the Animal Enterprise Terrorism Act of 2006 (AETA of 2006). The administrative agencies also launched several actions against radical environmental groups and their members which appears to have led to reductions in radical attacks within the United States. This chapter also discusses several legal precedents from U.S. law and reviews how the judicial branch applies the rules of AETA of 2006. Finally, we suggest that these radical environmentalist and animal right actors should not be treated as terrorists. Although research shows that strict regulations could successfully deter eco-offenders, we argue that the government should increase negotiations with environmental groups and animal rights advocates but not adopt punitive regulations to control their behavior.