President Obama's second inauguration is a historic occasion. This is the first presidential inauguration to fall on Martin Luther King, Jr. Day, an auspicious event for the first African-American president.
Of course, Obama is also now the first African-American president to win reelection.
Let's look at some other inauguration firsts throughout history.
In 2009, Obama's first inauguration was the largest inaugural ceremony in history, with more than 1.8 million people gathering to watch him take the oath of office. In fact, the inauguration was the largest event in the history of Washington, D.C., including Fourth of July fireworks and civil rights marches.
Obama was the first American born in Hawaii to be sworn in as president.
Bill Clinton's second inauguration in 1997 was the first inaugural ceremony to be broadcast live on the internet.
Ronald Reagan's second inauguration in 1985 was the coldest on record, at 7 degrees Fahrenheit. However, his first inauguration in 1981 was the warmest, at 55 degrees.
In 1977, Jimmy Carter became the first president to walk in the inaugural parade after the swearing-in ceremony.
In 1974, Gerald Ford became the first president to be sworn in without first being elected as either president or vice-president, after the Watergate scandal resulted in the resignations of both Vice President Spiro Agnew and President Richard Nixon.
In 1965, Lyndon Johnson became the first president to ride in a bulletproof limousine. Security was high following the 1963 assassination of John F. Kennedy.
At Kennedy's inauguration in 1961, the tradition of having a poet speak at the inauguration began. Robert Frost read a poem.
Harry S. Truman's second inauguration in 1949 was the first after World War II, and it was the first ceremony to be televised.
Franklin D. Roosevelt had been the only president sworn in four times, as he won election four times, before the Constitution was amended to limit presidents to two terms. In an interesting twist, President Obama now joins him. In 2009, Chief Justice John Roberts administered the oath of office incorrectly, so Obama took it again with the proper text.
Obama also took the oath on Sunday, which is the official day the new presidential term begins. But since the date fell on a Sunday, he will also take the oath a fourth time on Monday in the public ceremonies.