Boko Haram, a violent Islamist insurgent group originally based in northeast Nigeria, continues to wage a deadly campaign in Nigeria and neighboring countries in the Lake Chad Basin region. A State Department-designated Foreign Terrorist Organization since November 2013, the group drew widespread international attention for its April 2014 abduction of almost 300 schoolgirls as well as its subsequent pledge of allegiance to the Islamic State (IS, also known as ISIL or ISIS) in March 2015. More than 15,000 people are estimated to have been killed in Boko Haram violence—including more than 6,500 in 2015 alone—and the conflict has caused a humanitarian emergency around Lake Chad, displacing more than 2.4 million people and cutting off humanitarian access to thousands. Operations by regional forces, most notably those from Chad and Nigeria, reversed the territorial advances that Boko Haram made from mid-2014 into early 2015, when it took nominal control of large swathes of territory in northeastern Nigeria under a self-described Islamic caliphate. The group has since reverted to asymmetric attacks, largely against soft targets in northeastern Nigeria and northern Cameroon. Despite its loss of territory, Boko Haram maintains the ability to move and conduct attacks in an area that stretches from southern Niger's Diffa region south into northern Cameroon. The group has also demonstrated its ability to attack the Chadian capital, N'djamena, killing scores in multiple bombing incidents. Notably, there has been a significant increase over the past year in the use of suicide bombers, most of them women and children. Many observers assess that Nigeria's new head of state, Muhammadu Buhari, has taken a more proactive approach toward countering Boko Haram than his predecessor, President Goodluck Jonathan, who was widely criticized for what has been described as a mismanaged and heavy-handed response to Boko Haram. Nonetheless, the extent to which Nigerian security forces "control" territory reclaimed from the group remains subject to debate, and Nigeria and Cameroon have drawn criticism from human rights groups for alleged abuses against civilians by security forces during counterinsurgency operations. In view of the growing impact Boko Haram has had on neighboring Cameroon, Niger, and Chad, U.S. officials have increasingly sought to support programs to improve regional counterterrorism capabilities and coordination. This support is channeled through various regional programs and funding mechanisms, including the Global Security Contingency Fund (GSCF) and the Counterterrorism Partnership Fund (CTPF), as well as through bilateral security assistance. In total, Boko Haram-related counterterrorism assistance has totaled more than $400 million to date. The U.S. military has deployed surveillance assets and related personnel to the region to support regional efforts, and advisory support by U.S. military personnel is now reportedly under consideration for Nigeria. Additionally, the United States supports programs to counter violent extremism in the region, including more than $30 million in activities managed by the USAID Office of Transition Initiatives (OTI). The United States also provides substantial humanitarian aid for the Lake Chad Basin area, totaling almost $200 million in FY2015 and FY2016 to date. Congress and Obama Administration officials continue to weigh additional options for strengthening U.S.-Nigerian security relations in a manner that will curtail Boko Haram's violent campaign. This report explores several questions that have been often asked in relation to the group, the impact of its attacks, and the response of the Nigerian government and other international actors, including the United States. Boko Haram emerged in the early 2000s as a small Sunni Islamic sect advocating a strict interpretation and implementation of Islamic law for Nigeria. Calling itself Jama'a Ahl as-Sunna Li-da'wa wa-al Jihad (roughly translated from Arabic as "People Committed to the Propagation of the Prophet's Teachings and Jihad"), the group is more popularly known as Boko Haram (often translated as "Western education is forbidden"), a nickname given by local Hausa-speaking communities to describe the group's view that Western education and culture have been corrupting influences that are haram ("forbidden") under its conservative interpretation of Islam. In 2015, after pledging allegiance to the self-proclaimed Islamic State, the group sought to rebrand itself as the Islamic State's West Africa Province (ISWAP). While the sect's original leadership did not initially call for violence, its followers engaged in periodic skirmishes with Nigerian police during its formative years. At that time the group's activities were limited in scope and contained within several highly impoverished states in Nigeria's predominately Muslim northeast. In July 2009, at least 700 people were killed during an effort by Nigerian security forces to suppress the group. In the course of that violence, the group's leader, Mohammed Yusuf, a charismatic young cleric who had studied in Saudi Arabia, was killed in police custody. The group subsequently appeared to dissipate, but reemerged a year later under new leadership, orchestrating a large prison break in September 2010 that freed hundreds, including its own members. Some Boko Haram militants may have fled to insurgent training camps in the Sahel in 2009-2010. It is widely rumored that certain northern Nigerian politicians may have provided support and/or funding to the group in its early years, reportedly using them to exert influence or threaten rivals. The group built ties with transnational extremist groups in the region, notably Al Qaeda in the Islamic Maghreb (AQIM), which reportedly provided training and access to increasingly sophisticated weaponry. Boko Haram attacks since 2011 have featured improvised explosive devices (IEDs), car bombs, and suicide attacks, but fighters also continue to inflict a heavy toll using small arms and arson. The use of women and children as suicide bombers has become an increasing tactic since 2014, as is discussed below. By many accounts, Boko Haram is not a monolithic organization. Beyond its core militants, who appear to ascribe to a violent Sunni extremist ideology, the group appears to draw support from a broader group of followers, predominantly young men from northeast Nigeria and the border areas of southeast Niger and northern Cameroon. Experts speculate that some of the group's supporters may be driven by frustration with perceived disparities in the application of laws (including sharia ); the lack of development, jobs, and investment in the north; and/or the abusive response of security forces in the region. As such, observers contend that despite the group's nickname and expressed rejection of Western culture, Boko Haram's ideology encompasses a broader worldview that combines an exclusivist interpretation of Islam—which rejects not only Western influence but also democracy, constitutionalism, and more moderate forms of Islam—with "politics of victimhood" that resonate in Nigeria's underdeveloped northern states. Some of its fighters have reportedly been drawn into the group by financial incentive or under threat. U.S. officials have estimated in press reports that Boko Haram may have between 4,000 and 6,000 "hardcore" fighters, while other sources contend its force could be larger. By some accounts, the group may have lost some 30 percent of its fighting force during the 2015 regional offensive to reclaim territory from the insurgents. Boko Haram is reportedly led by a shura council, under the direction of Abubakar Shekau, who, like Yusuf, is an ethnic Kanuri (the predominant ethnic group in Borno state, where Boko Haram originated). What role Islamic State representatives may now play in the leadership structure is unclear. Some observers speculate that Shekau has been sidelined by IS central leadership and possibly replaced by a Libyan-based IS official from outside the region, although there has yet to be a noticeable shift in the group's tactics or targeting to suggest a leadership change. The emergence of a splinter faction, Ansaru, in early 2012 contributed to speculation about divisions within the group (see below). Ansaru's leaders, some of whom reportedly had direct links to AQIM and Al Qaeda, allegedly differed with Shekau in their interpretation of Islamic law and criticized his leadership and approach. Shekau led a purge against the faction in 2013 and some of its members reportedly reintegrated into Boko Haram; other Ansaru members may continue to work with other extremist groups in the Sahel region. Boko Haram has demonstrated significant operational flexibility in its nearly seven year insurgency. In July 2014, the group shifted from a tactical focus on asymmetric attacks (unconventional guerilla-style or terrorist strikes) against government and civilian targets, toward a conventional offensive to seize and hold territory. Estimates on the amount of territory held by Boko Haram vary, but press reports suggest that by early 2015 the Nigerian government may have lost between 40%-70% of Borno state and some territory in neighboring Yobe and Adamawa states, including border areas near Cameroon. Operations by regional forces, most notably those from Chad and Nigeria, reversed these territorial advances, retaking much of Boko Haram's self-described Islamic caliphate. The group has since reverted to asymmetric attacks, largely against soft targets in northeastern Nigeria and northern Cameroon, and maintains the ability to move and conduct attacks in an area that stretches from southern Niger's Diffa region south into northern Cameroon. The group has also demonstrated its ability to attack the Chadian capital, N'djamena, killing scores in multiple bombing incidents. Notably, there has been a significant increase over the past year in the use of suicide bombers, most of them women and children (see below). The area affected by Boko Haram is home to an estimated 30 million people.