To keep America safe from terrorists, customs and immigration agents must monitor 7,500 miles of land and sea borders, dozens of airports and 300 official ports of entry. They also monitor the 11 million trucks, 2.2 million rail cars and 7,500 foreign-flag ships that enter the country each year. And they oversee the 31 million non-citizens — mostly tourists — who visit each year. After Sept. 11, President Bush formed the Office of Homeland Security, and Congress passed sweeping legislation giving police and intelligence agencies more power to monitor U.S. borders. But experts disagree over which security steps would be most cost-effective and least disruptive to trade and Americans' daily lives. And civil libertarians warn that some proposed measures — such as linking driver's licenses to a national database and targeting certain ethnic groups — would undermine civil liberties.

Patrick Marshall is a freelance writer in Seattle, Wash., and contributing writer for CQ Researcher who writes about public policy and technology issues. He is a computer columnist for The Seattle Times and holds a BA in anthropology from the University of California at Santa Cruz and a master's in international studies from the Fletcher School of Law & Diplomacy at Tufts University.