This report analyzes homegrown violent jihadist plots and attacks that have occurred since 9/11. It discusses the radicalization process and the forces driving violent extremist activity. It examines post-9/11 law enforcement and intelligence efforts to combat terrorism and the challenges associated with those efforts. It also briefly discusses the building of trust and partnership between community groups and government agencies and the tensions that may occur between law enforcement and engagement activities. The report does not address terrorist activity against the United States conducted by foreigners largely radicalized abroad such as Quazi Mohammad Rezwanul Ahsan Nafis's attempt to blow up the Federal Reserve Bank of New York (2012), the Printer Cartridge plot (2010), the attempted airline bombing by Farouk Abdulmutallab (Christmas Day 2009), the Transatlantic Airliners plot (August 2006), or the "shoe bomber" Richard Reid (December 2001). Nor does the report address domestic terrorism attributed to violent extremists inspired by non-jihadist causes such as radical environmentalism, animal rights, or anti-abortion causes. Specific plots and attacks are described throughout the report to support analytical findings. A full description of each of the post-9/11 cases is provided in Appendix A of the report. "Homegrown" is the term that describes terrorist activity or plots perpetrated within the United States or abroad by American citizens, lawful permanent residents, or visitors radicalized largely within the United States. The term "violent jihadist" describes radicalized individuals using Islam as an ideological and/or religious justification for their belief in the establishment of a global caliphate—a jurisdiction governed by a Muslim civil and religious leader known as a caliph—via violent means. The Congressional Research Service (CRS) estimates that there have been 74 homegrown violent jihadist plots or attacks in the United States since September 11, 2001 (9/11). As part of a much-discussed apparent expansion of terrorist activity in the United States, from May 2009 through January 2014, arrests were made for 53 "homegrown," jihadist-inspired terrorist plots by American citizens or lawful permanent residents of the United States. Three of these resulted in attacks. Most of the 2009-January 2014 homegrown plots likely reflect a trend in jihadist terrorist activity away from schemes directed by core members of significant terrorist groups such as Al Qaeda. However, it may be too early to tell how sustained this uptick is. Regardless, the apparent spike in such activity after April 2009 suggests that ideologies supporting violent jihad continue to influence some Americans—even if a tiny minority. Homegrown violent jihadists may exhibit a number of conventional shortcomings when compared to international terrorist networks. Many homegrown violent jihadists possibly lack deep understanding of specialized tradecraft such as bomb making. They may not have the financing, training camps, support networks, and broad expertise housed in international organizations. These apparent shortcomings may keep some homegrown violent jihadists from independently engaging in large-scale suicide strikes. Because of this, they may turn to violence requiring less preparation, such as assaults using firearms. These shortcomings pose challenges for law enforcement, intelligence, and security officials charged with detecting, preventing, or disrupting terrorist plots. It is likely much harder to detect smaller conspiracies that can develop quickly. Individuals can become jihadist terrorists by radicalizing and then adopting violence as a tactic. "Radicalization" describes the process of acquiring and holding extremist, or jihadist beliefs . This activity is not necessarily illegal. For this report, "violent extremism" describes violent action taken on the basis of radical or extremist beliefs. For many, "violent extremism" is synonymous with "violent jihadist" and "jihadist terrorist." In other words, when someone moves from simply believing in jihad to illegally pursuing it via violent methods, he becomes a terrorist. Because the move from belief to violence is so individualized, there is no single path that individuals follow to become full-fledged terrorists. Intermediaries, social networks, the Internet, and prisons have been cited as playing key roles in the radicalization process. Intermediaries—charismatic individuals—often help persuade previously law-abiding citizens to radicalize or even become violent jihadists. Social networks, virtual or actual, support and reinforce the decisions individuals make as they embrace violent jihad, as does perusal of online materials. While there has been much discussion regarding the powerful influence online jihadist material may have on the formation of terrorists, no consensus has emerged regarding the Web and terrorism. Prisons, seen by some as potential hotbeds of radicalization, have not played a large role in producing homegrown jihadists. Homegrown violent jihadist activity since 9/11 defies easy categorization. No workable general profile of domestic violent jihadists exists. According to CRS analysis, the 74 plots since 9/11 exhibit four broad themes: a variety of endgames, relatively little stomach for suicide or martyrdom among plotters, successful attacks by lone wolves, and a wide range of capabilities among the plots. Endgames: In whole or in part, 33 plots involved individuals interested in becoming foreign fighters in conflict zones involving violent jihad abroad. Nineteen plots exclusively intended to use explosives or incendiary devices. Three exclusively intended to use or did use firearms. Twenty-seven plots incorporated multiple, unspecific, or unique tactics. Finally, outside of the 74 violent plots since 9/11, other schemes intended from the start only to fund or materially support the activities of their jihadist colleagues. Suicide or Martyrdom: According to publicly available information, 18 plots included individuals who clearly professed interest in killing themselves while engaged in violent jihad. Success of Lone Wolves: Lone wolves conducted four of the five successful homegrown attacks since 9/11. Divergent Capabilities: Among the 74 homegrown plots since 9/11, the operational capabilities of participants diverged greatly. Some evinced terrorist tradecraft such as bomb making skills. Others appeared to be far less experienced. The spate of arrests in recent years should not obscure the challenges facing law enforcement in disrupting homegrown terrorist plotting. Counterterrorism activity exists within two broad contexts. The first of these involves addressing radicalization, much of which occurs in the open marketplace of ideas. Please see CRS Report R42553, Countering Violent Extremism in the United States , for more on this topic. The second context—the focus of this report—is more "operational" and encompasses both violent jihadist plots (largely involving secretive illegal activity) and the police work used to dismantle them. The latter context, by necessity, also occurs outside of the public's view. Government efforts to combat domestic violent jihad straddle both of these arenas. In the post-9/11 environment, the public has expected law enforcement to adopt a proactive posture in order to disrupt terrorist plots before an attack occurs. Investigative leads about terrorist plots in the homeland may originate from foreign intelligence sources. But, for the most part, information about homegrown plots is available only through domestic intelligence activities. In order to proactively gather intelligence, law enforcement has adopted a preventive policing approach that focuses not just on crime that has occurred, but on the possibility that a crime may be committed in the future. In this context, a major challenge for law enforcement is gauging how quickly and at what point individuals move from radicalized beliefs to violence so that a terrorist plot can be detected and disrupted. At the federal level, the Department of Justice (DOJ) and the Federal Bureau of Investigation (FBI, the Bureau) implemented a forward-leaning approach with a revision to the Attorney General's Guidelines for Domestic FBI Operations. The revision, meant to streamline the FBI's investigations and make them more proactive, has spurred the use of an investigative tool dubbed "assessments." These allow for the investigation of individuals or groups without factual predication. The revised guidelines have, however, generated some controversy among civil libertarians. Also critical among the proactive approaches employed by law enforcement is the monitoring of Internet and social networking sites. The USA PATRIOT Act ( P.L. 107-56 ) authorizes the FBI to use National Security Letters to obtain a range of information including data pertaining to email and Internet use. It appears that U.S. law enforcement has effectively exploited the Internet—which radicalizing individuals can mine for information and violent jihadists use while plotting—in its pursuit of terrorists. A review of criminal complaints and indictments in terrorism cases reveals that the FBI has exploited the Internet and/or email communications to build cases against defendants in at least 36 of the post-9/11 cases studied in this report. Although much is said about terrorist use of the Internet for recruitment, training, and communications, these cases suggest that terrorists and aspiring terrorists will not find the Internet to be a uniformly permissive environment. The role of state, local, and tribal law enforcement in detecting nascent terrorist plotting is particularly important, especially considering the challenges involved in detecting lone wolves and homegrown jihadist groups with few connections to larger terrorist organizations. More than a decade after the 9/11 attacks, integrating state, local, and tribal law enforcement into the national counterterrorism effort continues to be an abiding concern of policymakers. DOJ and the FBI have established Joint Terrorism Task Forces (JTTFs) to help coordinate federal, state, and local investigative activities. States and major urban areas have also established intelligence fusion centers with federal agencies, in part to share intelligence. The Nationwide Suspicious Activity Report Initiative (NSI) is a program to push terrorism-related information generated locally between and among federal, state, local, and tribal levels via fusion centers. To counter violent jihadist plots, U.S. law enforcement has employed two tactics that have been described as the "Al Capone" approach and the use of "agent provocateurs."