Many experts have postulated that the threat of attack with chemical, biological, radiological and nuclear (CBRN) weapons represents one of the greatest threats to U.S. national security. There is widespread agreement—within the U.S. government, among national security policy analysts, and across the political spectrum—that the United States faces a growing threat from the potential use of these weapons by hostile nations and terrorist groups. Many in Congress have also expressed concerns about the potential terrorist use of CBRN weapons and have supported U.S. efforts to address and mitigate this threat. President George W. Bush highlighted this threat in his 2002 National Strategy to Combat Weapons of Mass Destruction. This report opened with the observation that "weapons of mass destruction (WMD)—nuclear, biological, and chemical—in the possession of hostile states and terrorists represent one of the greatest security challenges facing the United States. We must pursue a comprehensive strategy to counter this threat in all of its dimensions." President Obama offered a similar warning in his 2010 National Security Strategy, when he noted that "there is no greater threat to the American people than weapons of mass destruction, particularly the danger posed by the pursuit of nuclear weapons by violent extremists and their proliferation to additional states." The United States uses a range of policy tools to address the threats posed by the potential spread of nuclear, chemical, and biological weapons to hostile nations or non-state actors. These range from diplomatic engagement and economic sanctions to the threat of military intervention. One key set of tools is a set of financial and technical programs known, variously, as cooperative threat reduction programs, nonproliferation assistance, or, global security engagement. Through these programs, the United States seeks to work with other nations to help them secure and eliminate their CBRN weapons and material, to stem the flow of weapons and related knowledge and materials to hostile nations or non-state actors who might seek to develop their own weapons, and to develop training programs and share "best practices" to ensure that other nations can protect the materials and knowledge that remain in their countries. Many of the programs that are funded through these efforts evolved out of an initiative that Congress created in late 1991. After an August 1991 coup in Moscow led to concerns about the potential loss of control over Soviet nuclear weapons, Congress passed the Nunn-Lugar amendment and authorized the use of up to $400 million in funds in the Department of Defense (DOD) budget to help safely secure, transport, and eliminate Soviet nuclear weapons. This initiative grew over the years, such that the United States spent around $1.65 billion in FY2013 on programs that have sought to secure and eliminate nuclear, chemical, and biological weapons and materials in the former Soviet states; enhance border security and export controls to deter and detect efforts to transport these materials across state lines; secure and eliminate nuclear, chemical, or biological materials in nations outside the former Soviet Union; and redirect weapons scientists in many nations around the world so that they will pursue programs with peaceful purposes. This funding has, however, begun to decline, falling to $1.59 billion in FY2014, $1.25 billion in FY2015, and a requested $1.4 billion in FY2016. In addition, these programs are now funded and administered by DOD, the Department of Energy (DOE), the State Department, the Department of Homeland Security (DHS), and several other U.S. agencies. Over the years, Congress has offered significant support to these efforts. It has not only authorized and appropriated increasing sums for these programs, it has generally agreed with the executive branch on the priorities and goals for them. Nevertheless, over the years, some Members have questioned the value of specific goals and the effectiveness of some projects. Congress has adjusted the profile of these programs over the years, sometimes reducing funds, sometimes increasing funds, and sometimes initiating new programs and project areas. The 113 th Congress is likely to continue to review the funding for these programs, consider the goals, and assess their effectiveness. Moreover, Congress may continue to raise questions about the future intent of these programs, the success of government-wide coordination in implementing them, and the extent of international cooperation in addressing these threats. These questions may be amplified in the future, as the United States and Russia conclude most of their cooperation. This report provides information on the wide range of programs that the United States is pursuing to secure and eliminate nuclear, chemical, and biological weapons and materials and to prevent hostile nations and terrorist organizations from gaining access to these weapons or the knowledge and materials needed to manufacture and use them. It begins with a brief review of the evolution of these programs, demonstrating how the goals and objectives have changed over the years. It also reviews some of the issues that Congress may confront as it seeks to provide oversight of these programs and reviews budget requests for them. The report then provides information on individual programs that are designed to secure and eliminate nuclear weapons, secure and eliminate nuclear materials, secure borders and improve export controls, eliminate chemical weapons, secure biological pathogens, and redirect scientists with knowledge of CBRN weapons. Congress initiated U.S. threat reduction and nonproliferation assistance to the Soviet Union in November 1991. A failed coup in Moscow in August 1991 and the subsequent disintegration of the Soviet Union had raised concerns about the safety and security of Soviet nuclear weapons. Consequently, Senators Sam Nunn and Richard Lugar proposed an amendment to the implementing legislation for the Conventional Armed Forces in Europe (CFE) Treaty ( P.L. 102-228 ). This amendment, titled the "Soviet Nuclear Threat Reduction Act of 1991," authorized the use of $400 million in FY1992 Defense Department (DOD) funds to assist the Soviet Union, and its "successor entities" with efforts to "1) destroy nuclear weapons, chemical weapons, and other weapons, 2) transport, store, disable, and safeguard weapons in connection with their destruction, and 3) establish verifiable safeguards against the proliferation of such weapons." This effort became known as the Cooperative Threat Reduction (CTR) Program. Initially, many in Congress saw U.S. assistance under the CTR program as an emergency response to impending chaos in the Soviet Union. Senators arguing in support of the program, including Senators Nunn and Lugar, noted that the disintegration of the Soviet Union created "the danger that the ultimate disposition of nuclear weapons in the new political system will not be conducive to their safety or international stability." They warned of "a danger of seizure, theft, sale or use of nuclear weapons or components" and argued that "any weakening of control over weapons and components could spill outside the territory of the former Soviet Union, fueling nuclear proliferation worldwide." Senator Nunn further warned that "we are on the verge of either having the greatest destruction of nuclear weapons in the history of the world or the greatest proliferation of nuclear weapons, nuclear materials, and scientific know-how on how to make these weapons, as well as chemical weapons, ballistic missiles, even biological weapons the world has ever seen." Even after the sense of immediate crisis passed in 1992 and 1993, many analysts and Members of Congress remained concerned about the potential for diversion or a loss of control of Russia's nuclear and other weapons. Russia's economy was extremely weak and press accounts reported that nuclear materials from Russia were appearing on the black market in Western Europe. Consequently, many began to view CTR as a part of a long-term threat reduction and nonproliferation effort. Former Secretary of Defense William Perry referred to CTR as "defense by other means," as the program helped eliminate Soviet weapons that had threatened the United States and contain weapons and materials that could pose new threats in the hands of other nations. By the mid-1990s, many observers also began to view U.S. assistance to the former Soviet states as a part of the effort to keep weapons of mass destruction away from terrorists. In 1996, experts testified to Congress that Russian nuclear and chemical facilities, with their crumbling security and lack of accounting procedures, could provide a source for terrorists seeking nuclear or chemical materials. In response, Congress expanded the programs that provided security at facilities with nuclear materials and suggested that more attention be paid to security at facilities with materials that could be used in chemical or biological weapons. In January 2001, a task force sponsored by the Department of Energy stated that "the most urgent unmet national security threat to the United States today is the danger that weapons of mass destruction or weapons-usable materials in Russia could be stolen and sold to terrorists or hostile nation states and used against American troops abroad or citizens at home." Since September 11, 2001, virtually all analysts who follow U.S. threat reduction and nonproliferation assistance have argued that, by helping Russia protect its weapons, related materials, and knowledge, the United States could make it more difficult for terrorists to acquire CBRN weapons. The George W. Bush Administration clearly considered U.S. threat reduction and nonproliferation programs in the former Soviet states to be a part of U.S. efforts to keep weapons of mass destruction away from terrorists, explaining, in early 2003, that it had "expanded the strategic focus of the CTR program" to support the war on terrorism. In its budgets presented in the years after FY2004, the Administration increased funding for several export and border control programs, for programs designed to stem the leakage of knowledge out of the former Soviet Union, and for an effort to find and recover "radiological sources"—a type of device that could provide terrorists with nuclear materials for use in a "dirty bomb." All of these initiatives focused more on stemming proliferation than on eliminating nuclear weapons in the former Soviet states. But the programs did not completely lose the initial focus. During a February 2005 summit in Bratislava, Presidents Bush and Vladimir Putin agreed to accelerate some of the efforts to secure Soviet-era nuclear weapons. This agreement shifted additional funding into some of the DOD CTR projects and hastened the completion of some warhead storage and security efforts.