From the Summary: "The Visa Waiver Program (VWP), originally established in 1986 as a trial program and made permanent in 2000 (P.L. 106-396), allows nationals from 39 countries, many of which are in Europe, to enter the United States as temporary visitors (nonimmigrants) for business or pleasure without first obtaining a visa. Generally, temporary visitors for business or pleasure from non-VWP countries must obtain a visa from Department of State (DOS) officers at a consular post abroad before traveling to the United States. Some observers argue that the VWP strengthens national security because it sets standards for travel documents, requires information sharing between the member countries and the United States on criminal and security concerns, and mandates reporting of lost and stolen travel documents. VWP travelers have to present e-passports (i.e., passports with a data chip containing biometric information), which tend to be more difficult to alter than other types of passports. Nevertheless, some observers of the program have raised concerns about the possibility that terrorists will enter the United States under the VWP because those entering under the VWP undergo a biographic, rather than a biometric (i.e., fingerprint and digital photograph),security screening and do not need to interview in person with a U.S. consular official before embarking for the United States."
CRS Report for Congress, RL32221
Congressional Research Service: https://crsreports.congress.gov/