The federal government's role in protecting U.S. citizens and critical infrastructure from cyber attacks has been the subject of recent congressional interest. Critical infrastructure commonly refers to those entities that are so vital that their incapacitation or destruction would have a debilitating impact on national security, economic security, or the public health and safety. This report discusses selected legal issues that frequently arise in the context of recent legislation to address vulnerabilities of critical infrastructure to cyber threats, efforts to protect government networks from cyber threats, and proposals to facilitate and encourage sharing of cyber threat information among private sector and government entities. This report also discusses the degree to which federal law may preempt state law.