Facilities handling large amounts of potentially hazardous chemicals (i.e., chemical facilities) might be of interest to terrorists, either as targets for direct attacks meant to release chemicals into the community or as a source of chemicals for use elsewhere. Because few terrorist attacks have been attempted against chemical facilities in the United States, the risk of death and injury in the near future is estimated to be low, relative to the likelihood of accidents at such facilities or attacks on other targets using conventional weapons. For any individual facility, the risk is very small, but risks may be increasing with potentially severe consequences for human health and the environment. Available evidence indicates that many chemical facilities may lack adequate safeguards. Two federal environmental laws enacted in 1986 and 1990 require chemical facility planning to protect the general public from accidental releases of hazardous chemicals. However, neither law explicitly addresses terrorism. After 9/11, Congress enacted legislation that requires the Department of Homeland Security (DHS) to analyze vulnerabilities and to suggest security enhancements for "critical infrastructure." The Public Health Security and Bioterrorism Preparedness and Response Act of 2002 (P.L. 107-188) and the Maritime Transportation Security Act (MTSA, P.L. 107-295) require vulnerability assessments and emergency response plans for some chemical facilities which supply drinking water or are located in ports, as well as security plans for chemical facilities in ports. Many other chemical facilities, including wastewater treatment facilities, remain unregulated. Congress might choose to rely on existing efforts in the public and private sectors to improve chemical site security over time. Alternatively, Congress could expand existing environmental planning requirements for chemical facilities to require consideration of terrorism. DHS could be directed to oversee security enhancement at potentially dangerous facilities. Or, Congress might enact legislation to reduce risks, either by "hardening" defenses against terrorists, for example by increasing security patrols, or by requiring industries to consider use of safer chemicals, procedures, or processes. Restricting terrorists' access to information might be a least-cost approach to reducing risks, but it would also limit public access to information about risks to which they might be exposed, and reduce accountability of facility owners. In the 109th Congress, two House bills would require designated facilities to prepare vulnerability assessments and plans for increasing facility safety and/or security and for responding in the event of an emergency. H.R. 1562 would require submission of assessments and plans to DHS, while H.R. 2237 would require submission to EPA. H.R. 2237 also would require consideration and use of "safer" technologies. No similar legislation has yet been introduced in the Senate, but it approved a "Sense of the Senate" that enforceable federal standards should be established to protect chemical facilities against a terrorist attack. Other bills (S. 2052/H.R. 713 and S. 1995) aim to enhance security for agricultural businesses and wastewater treatment facilities. This report will be updated as warranted by congressional activity.