The Islamic State (IS, aka the Islamic State of Iraq and the Levant, ISIL/ISIS, or the Arabic acronym Da'esh) is a transnational Sunni Islamist insurgent and terrorist group that controlled large areas of Iraq and Syria from 2014 through 2017. The group attracted a network of global supporters and its leader, Abu Bakr al Baghdadi, received pledges of affiliation from groups in several other countries. A series of terrorist attacks attributed to the group or to individuals it has inspired have claimed hundreds of lives on four continents since November 2015, including in the United States. While U.S. and allied forces in 2017 and 2018 successfully liberated most of the territory formerly held by the group in Syria and Iraq, IS leadership remains at large and IS fighters appear to be evolving into an insurgent force. The group's international affiliates continue to operate, and individuals inspired by the group continue to attempt attacks in Europe and elsewhere. The stabilization of areas recovered from the group in Iraq and Syria remains an ongoing challenge, and a U.S. military spokesperson for the counter-IS campaign warned in August 2018 that, "We cannot emphasize enough that the threat of losing the gains we have made is real, especially if we are not able to give the people a viable alternative to the ISIS problem." Members of Congress, executive branch officials, and their international counterparts continue to debate a range of proposals for consolidating battlefield gains made to date and preventing the Islamic State from succeeding in its stated objectives of remaining and expanding. President Obama's goals for U.S. strategy were to degrade and ultimately defeat the Islamic State through U.S. direct military action and support for local partner forces. President Donald Trump directed his Administration to develop a comprehensive plan to defeat the group and has accelerated U.S. military operations while augmenting U.S. contributions to stabilization in liberated areas. The U.S. military continues to conduct operations against the group in Iraq, Syria, and Afghanistan, while monitoring and occasionally striking its affiliates and personnel elsewhere. Parallel U.S. assistance efforts support stabilization in areas once held by the group, and diplomatic efforts have promoted political reconciliation among local factions in countries where Islamic State supporters are active. The United States also provides security assistance to partner governments in support of operations against Islamic State affiliates and to strengthen the ability of partners to deter and respond to Islamic State attacks. Evolving counterterrorism cooperation and intelligence sharing efforts among a wider network of concerned governments seek to further limit the ability of IS supporters to carry out transnational terrorist attacks. Interrelated conflicts and political crises in Iraq, Syria, and other countries where the Islamic State operates complicate efforts to address and durably eliminate the threats posed by the group. Military operations may reduce the numbers of IS fighters and liberate IS-held territory, but the underlying political disputes and development challenges that the Islamic State has exploited may create ongoing openings for the group if governance and reconstruction needs go unmet. Governments may continue to face difficult decisions about the potential risks and rewards of various military, law enforcement, surveillance, intelligence sharing, financial, border security, refugee admission, and consular countermeasures. This report provides background on the Islamic State organization, discusses its goals, operations, and affiliates, reviews U.S. legislative and policy debates, and reviews relevant legislation from the 114th and 115th Congresses.