• Extremist animal-rights group whose main bases of operation are Canada, the United Kingdom, and the United States
• Advocates vandalism, sabotage, and arson "to bring about animal liberation"
• Between 1997 and 2003, ALF caused, in conjunction with the Earth Liberation Front, $43 million in property damage.

The Animal Liberation Front (ALF) is an extreme animal rights organization that is classified as a terrorist group by the FBI. ALF identifies its main bases of operation as Canada, the United Kingdom, and the United States; all told, it is currently active in about twenty countries worldwide. ALF's self-defined mission is "to effectively allocate resources (time and money) to reduce animal suffering in the world." Toward this end, ALF states that it "carries out direct action against animal abuse in the form of rescuing animals and causing financial loss to animal exploiters, usually through the damage and destruction of property." Counted among these "exploiters" are hunters, fishers, butchers, factory farmers, restaurateurs, and those who use animals to entertain the public (in zoos, circuses, and rodeos). The fur, meat, egg, and dairy industries are also viewed as major offenders, as are scientists and technicians involved in laboratory animal testing. All of these pursuits, charges ALF, "profit from the misery and exploitation of animals." In ALF's estimation, the use of animals as sources of food, clothing, entertainment, or scientific knowledge is immoral and should be prevented by any means necessary. 

ALF candidly acknowledges that in its quest to force "animal abuse companies" out of business, it takes "illegal actions ... to bring about animal liberation." Adds ALF, "These are usually one of two things: rescuing animals from laboratories or other places of abuse, or inflicting economic damage on animal abusers." Economic damage is generally inflicted by means of theft, vandalism, arson, and sabotage. Because these activities are unlawful, ALF activists work anonymously, generally in cells of two to five people but sometimes alone. ALF has no formal hierarchy, central organization, leaders, newsletter, or official membership rolls. "Anyone who carries out direct action according to ALF guidelines," its website explains, "is a member of the ALF." The lone lifestyle stipulation is that in order to be recognized and supported by ALF, an individual must be either a vegetarian or a vegan.

Whenever an individual commits an illegal act in the name of ALF, he or she publicizes the incident by contacting one of the ALF press officers (at the North American Animal Liberation Press Office) or posting notice of his or her action on the ALF website. ALF's press office in the United States is run by Dr. Steven Best, a tenured professor and chairman of the philosophy department at the University of Texas El Paso.

ALF has its historical roots in the Hunt Saboteurs Association (HSA), an organization whose members try to save animals from hunters by laying false scents and blowing hunting horns to send hunters' hounds running in the wrong direction; disabling animal traps; setting off smoke bombs to disrupt hunting activities; and in some cases becoming human shields, placing themselves between hunters and the animals they are tracking.

In 1972, HSA activists Ronnie Lee and Cliff Goodman broke away from this organization and created a more militant group called the Band of Mercy. In 1974 Lee and Goodman firebombed a vivisection research center in England; both men served a year in prison for this act. After his apprehension, Lee proudly explained that he had participated in the firebombing to "prevent the torture and murder of our animal brothers and sisters." Following his release from prison, Lee was more militant than ever. He organized a new liberation campaign composed of thirty activists, and in 1976 he named his project the Animal Liberation Front.

The precise date of ALF's first American action is impossible to pinpoint, but one of the earliest was a 1979 incident where vandals broke into the New York University Medical School and released (or "liberated") five animals slated for experimental use. During the ensuing years, hundreds of similar "liberations" would take place. Among the animals that ALF activists have released from research facilities are dolphins, dogs, cats, guinea pigs, and monkeys.

In 1993 the Departments of Justice and Agriculture issued a report to Congress on the "effects of terrorism on enterprises which use animals," naming ALF as the most significant "radical fringe" animal rights group in the United States. The report stated that between 1979 and 1993, more than 300 incidents of break-ins, vandalism, arson and thefts had been committed in the name of animal rights nationwide. After some ALF members set a fire causing $3.5 million in damages at a veterinary lab in California in 1987, the FBI officially added ALF to its list of domestic terrorist organizations. According to the FBI, between 1995 and 2005 ALF committed some 700 criminal acts.

Between 1997 and 2003, ALF reportedly caused, in conjunction with the radical Earth Liberation Front, approximately $43 million in property damage. The two groups have conducted numerous direct actions jointly. In testimony given in 2004, John E. Lewis, Deputy Assistant Director of the FBI's counterterrorism division, stated that during the preceding ten years groups like ALF and ELF had engaged in more than 1,000 criminal acts and had caused more than $100 million in damage.

To educate animal-rights devotees in its methods and philosophy, ALF has produced a publication titled The ALF Primer, which teaches, in step-by-step detail, aspiring activists how to most effectively carry out their illegal deeds; i.e., cause maximum damage without being detected.

Among the more notable eco-terrorists associated with ALF in recent years is Gary Yourofsky.