While Americans have been targets of terrorist attacks for quite some time, September 11, 2001, awoke the nation to the reality of the threat of terrorism. The U.S. is now faced with the challenge of guarding against terror attacks while continuing to function as a vibrant economic and political community. The current threat environment requires greater engagement with the public, as the necessary eyes and ears of the nation's homeland security infrastructure. However, to be effective, the public must be equipped with the knowledge of where and why specific locations and activities may be a terrorist target, what is being done to protect those targets, and how they can help. The chapters of each volume of "Homeland Security" revolve around a core of central questions. Is the U.S. public safer today than pre-9/11? What are the threats, and what new threats have developed since 9/11? How can ports of entry be successfully monitored? Volume 1, "Borders and Points of Entry", addresses the question of how and where harmful people or material can enter the country, and how a combination of local, state, and federal agencies work with the private sector to ensure our security. Volume 2, "Public Spaces and Social Institutions", covers a wide variety of potential vulnerabilities. Volume 3, "Critical Infrastructure", deals with vital infrastructures and systems, attacks against which would yield not only significant loss of life but would also entail devastating economic and financial consequences.