Common values, overlapping interests, and shared goals are the foundation of what is often described as the transatlantic partnership between the United States and Europe. Many observers stress that in terms of security and prosperity the United States and Europe have grown increasingly interdependent. Both sides of the Atlantic face a common set of challenges, including a broad range of economic concerns as well as terrorism, nuclear proliferation, and armed conflict or other forms of instability in many parts of the world. Both sides are proponents of democracy, open societies, human rights, and free markets. Supporters of close U.S.-European cooperation argue that neither the United States nor Europe can adequately address the wide array of global concerns alone, and that the track record shows the two sides can accomplish much more when they work together. The United States and Europe also share a huge and mutually beneficial trade and investment relationship. This report summarizes key areas of shared interest and cooperation and highlights some of the main challenges in the transatlantic relationship. The activities of the U.S. Congress frequently involve issues that have a European dimension, including economic, security, and diplomatic issues. Members of Congress often interact directly with European legislators and officials to discuss a wide variety of topics. In the course of legislative activities or in exercising oversight of U.S. foreign policy, Members of Congress may choose to consider the dynamics of U.S.-European cooperation in terms of benefits versus shortcomings, alignment versus divergence, or partnership versus competition. Many Members of Congress have long supported a close transatlantic relationship and have seen the European Union (EU), the North Atlantic Treaty Organization (NATO), and the idea of a Europe "whole and free" as supporting and advancing U.S. interests. During the Cold War, many viewed a more integrated and united Europe as a way to counter the Soviet Union. More recently, congressional interest in Europe tends to be rooted in a U.S. need for like-minded partners in facing global challenges. At various times over the years, however, Members have also been concerned when U.S. and European policy positions have conflicted, have doubted the degree of cooperation offered by Europe, or have questioned whether Europe might somehow constrain U.S. policy choices. By almost any measure, the institutional pillars of the Euro-Atlantic community, NATO and the EU, have proven successful in promoting prosperity and security in Europe. The U.S. Congress and successive U.S. Administrations have strongly supported both institutions as means to foster democratic states, reliable military allies, and strong trading partners. While strong bilateral relationships between the United States and individual European countries remain a vital foundation for transatlantic relations, the relationship between the United States and the EU has been taking on a growing significance. The EU has become an increasingly important interlocutor for the United States because its 28 member countries now take common decisions and formulate common policies in a wide range of areas, including many economic and social issues and a growing number of law enforcement and judicial matters, at the level of the EU institutions. The EU is also continuing efforts to develop a stronger Common Foreign and Security Policy (CFSP) and Common Security and Defense Policy (CSDP). Meanwhile, NATO remains the preeminent security institution of the Euro-Atlantic community. Given the United States' leading role in the Atlantic alliance, Members of Congress maintain a consistent and significant interest in NATO. Like the EU, NATO has experienced dramatic change over the past two decades. Since the end of the Cold War, the alliance has added 12 new member states from Central and Eastern Europe. While the last decade has been defined largely by operations in Afghanistan, the member states of the alliance have also continued long-term discussions about the future role and capabilities of NATO. Over the past year, the conflict in Ukraine and tense relations with Russia have become central factors in these discussions. The year 2014 was one of leadership transitions for the Euro-Atlantic institutions. In May, EU-wide elections selected 751 Members of the European Parliament (MEP) to a new five-year term. German MEP Martin Schulz of the Socialists and Democrats group was reelected for a second term as President of the Parliament. Former Norwegian Prime Minister Jens Stoltenberg replaced Anders Fogh Rasmussen as the new Secretary General of NATO in October. In November, the 28 commissioners of a new European Commission took office for a term of five years. After 10 years under the leadership of Jose Manuel Barroso, former Luxembourg Prime Minister Jean-Claude Juncker took over as President of the Commission. Former Italian Foreign Minister Federica Mogherini replaced Catherine Ashton as the EU's High Representative for Foreign Affairs and Security Policy. In December, former Polish Prime Minister Donald Tusk became the new President of the European Council, replacing Herman Van Rompuy. Polls show that European perceptions of U.S. foreign policy under the Obama Administration remain relatively favorable, and considerably more positive compared to the years of the George W. Bush Administration. The overall tone of transatlantic relations has been mostly constructive over the past six years, and many of the broad global challenges faced by the United States and Europe have pushed the two sides toward common or cooperative approaches. In attempting to deal jointly with the daunting list of challenges they face, however, both sides have also encountered frustrations and reality checks that have reminded each side to be realistic about what it can expect from the other. After the Obama Administration announced in 2012 a "re-balancing" of U.S. foreign policy toward a greater focus on Asia, many Europeans expressed anxiety about the United States pulling back from Europe. The crisis and conflict in Ukraine has since caused U.S. policy makers to rethink many assumptions about European security, and the United States continues to play a leading role in NATO and managing relations with Russia. Given that much of U.S. attention is also likely to remain centered on Asia and the Middle East, general U.S. hopes and expectations are that Europe should share a significant part of the burden when it comes to its own security, take a leading role on most regional and some other international issues, and continue to act as an effective partner in addressing a wide range of common threats and concerns. Most examples of transatlantic cooperation are largely positive, but in assessing the long-term dimensions of the partnership many U.S. officials remain concerned by Europe's ongoing economic difficulties, continuing declines in defense spending and military capabilities, and questions about Europe's ability to deliver a robust and coherent common foreign policy. U.S. officials and Members of Congress assessing the partnership with Europe also face complex and changing political dynamics within the EU and its member states. The European financial and debt crisis that followed the 2008-2009 global downturn has forced European leaders to confront the fundamentally unfinished nature of the EU. Although leaders took a number of unprecedented measures in response to the crisis, the process of arriving at these reforms highlighted diverging preferences and outlooks that caused tensions between EU member states. Although the crisis appears to have receded, there is a sense that its underlying causes remain unresolved and that basic questions about the future of further EU integration remain unanswered. At the same time, the perceived inability of Europe's traditional mainstream parties to solve economic and social problems has led to an anti-establishment backlash among European voters. In many countries, relatively new political parties are gaining strength, many of them populist parties advocating far-right and far-left policies. While such parties tend to variously embrace forms of nationalist, anti-immigration, or anti-Islam policies, nearly all are anti-EU to some degree, whether in terms of opposing the euro currency, further European integration, or even their country's membership in the union. "Euro-skeptic" parties of the far-right and far-left won approximately one quarter of the votes in the May 2014 European Parliament election. Following the victory of the radical-left Syriza party in the January 2015 Greek elections, the strength of this trend will be further tested over the course of the year with national elections in Estonia, Finland, Denmark, Portugal, Poland, Spain, and the United Kingdom. The UK elections, in particular, are expected to have major implications related to a possible national referendum on the EU membership of the country frequently regarded as the United States' closest European ally. In various ways, European domestic challenges, including political instability, economic struggles, social unrest, and growing skepticism about the EU could affect Europe's ability to act in partnership with the United States. The deterioration of U.S. and European relations with Russia became a predominant issue in 2014. For U.S. and European policy makers, developments stemming from the crisis and conflict in Ukraine have transformed Russia from a difficult but important "strategic partner" into a "strategic problem" of uncertain dimensions. While some officials and observers continue to advocate the importance of pragmatic cooperation with Russia where possible, others suggest that given recent Russian actions, a return to previous levels of cooperation remains a long way off. For more than a decade, relations between Russia and the West have been marked by points of tension. Russian policy makers viewed NATO enlargement and U.S.-European support for Kosovo's independence with resentment, and the 2008 conflict between Russia and Georgia brought relations to a new low. The Obama Administration came to office seeking to improve relations, however, and after a "reset" initiative, U.S.-Russia cooperation on Afghanistan and Iran improved, the two sides signed the New START treaty, and the revision of U.S. missile defense plans temporarily diminished tensions on that issue. At the same time, U.S. and European objections remained regarding Russia's policy on numerous issues, including its recognition of Georgia's Abkhazia and South Ossetia regions as independent countries and the unilateral suspension of its obligations under the Conventional Armed Forces in Europe (CFE) Treaty.