Jimmy Carter's tenure as the 39th president of the United States began with his inauguration on January 20, 1977, and ended on January 20, 1981. A Democrat from Georgia, Carter took office after defeating incumbent Republican President Gerald Ford in the 1976 election. His presidency ended following his defeat in the 1980 election by Republican Ronald Reagan.

Carter took office during a period of "stagflation," as the economy experienced a combination of high inflation and slow economic growth. His budgetary policies centered on taming inflation by reducing deficits and government spending. Responding to energy concerns that had persisted through much of the 1970s, his administration enacted a national energy policy designed to promote energy conservation and the development of alternative resources. Despite Carter's policies, the country was beset by an energy crisis in 1979, which was followed by a recession in 1980. Carter sought reforms to the country's welfare, health care, and tax systems, but was largely unsuccessful, partly due to poor relations with Congress.

Taking office in the midst of the Cold War, Carter reoriented U.S. foreign policy towards an emphasis on human rights. He continued the conciliatory Cold War policies of his predecessors, normalizing relations with China and pursuing further Strategic Arms Limitation Talks with the Soviet Union. In an effort to end the ArabIsraeli conflict, he helped arrange the Camp David Accords between Israel and Egypt. Through the TorrijosCarter Treaties, Carter guaranteed the eventual transfer of the Panama Canal to Panama. After the Soviet invasion of Afghanistan, he discarded his conciliatory policies towards the Soviet Union and began a period of military build-up and diplomatic pressure such as pulling out of the Moscow Olympics.

The final fifteen months of Carter's presidential tenure were marked by several additional major crises, including the Iran hostage crisis and economic malaise. Ted Kennedy, a prominent liberal Democrat who protested Carter's opposition to a national health insurance system, challenged Carter in the 1980 Democratic primaries. Boosted by public support for his policies in late 1979 and early 1980, Carter rallied to defeat Kennedy and win re-nomination. In the general election, Carter faced Reagan, a conservative former governor of California. Reagan won a decisive victory. In polls of historians and political scientists, Carter is usually ranked as a below-average president, but is seen more positively through his post-presidency humanitarian activities across the globe.

The president of the United States (POTUS) is the head of state and head of government of the United States of America. The president directs the executive branch of the federal government and is the commander-in-chief of the United States Armed Forces.

The power of the presidency has grown substantially since the office's establishment in 1789. While presidential power has ebbed and flowed over time, the presidency has played an increasingly strong role in American political life since the beginning of the 20th century, with a notable expansion during the presidency of Franklin D. Roosevelt. In contemporary times, the president is also looked upon as one of the world's most powerful political figures as the leader of the only remaining global superpower. As the leader of the nation with the largest economy by nominal GDP, the president possesses significant domestic and international hard and soft power.

Article II of the Constitution establishes the executive branch of the federal government and vests the executive power in the president. The power includes the execution and enforcement of federal law and the responsibility to appoint federal executive, diplomatic, regulatory, and judicial officers. Based on constitutional provisions empowering the president to appoint and receive ambassadors and conclude treaties with foreign powers, and on subsequent laws enacted by Congress, the modern presidency has primary responsibility for conducting U.S. foreign policy. The role includes responsibility for directing the world's most expensive military, which has the second largest nuclear arsenal.

The president also plays a leading role in federal legislation and domestic policymaking. As part of the system of checks and balances, Article I, Section 7 of the Constitution gives the president the power to sign or veto federal legislation. Since modern presidents are also typically viewed as the leaders of their political parties, major policymaking is significantly shaped by the outcome of presidential elections, with presidents taking an active role in promoting their policy priorities to members of Congress who are often electorally dependent on the president. In recent decades, presidents have also made increasing use of executive orders, agency regulations, and judicial appointments to shape domestic policy.

The president is elected indirectly through the Electoral College to a four-year term, along with the vice president. Under the Twenty-second Amendment, ratified in 1951, no person who has been elected to two presidential terms may be elected to a third. In addition, nine vice presidents have become president by virtue of a president's intra-term death or resignation. In all, 45 individuals have served 46 presidencies spanning 58 full four-year terms.Joe Biden is the 46th and current president of the United States, having assumed office on January 20, 2021.