The first inauguration of Barack Obama as the 44th President of the United States took place on Tuesday, January 20, 2009. The inauguration, which set a record attendance for any event held in Washington, D.C., marked the commencement of the first four-year term of Barack Obama as President and Joe Biden as Vice President. Based on the combined attendance numbers, television viewership, and Internet traffic, it was among the most-observed events ever by the global audience.

A New Birth of Freedom, a phrase from the Gettysburg Address, served as the inaugural theme to commemorate the 200th anniversary of the birth year of Abraham Lincoln. In his speeches to the crowds, Obama referred to ideals expressed by Lincoln about renewal, continuity and national unity. Obama mentioned these ideals in his speech to stress the need for shared sacrifice and a new sense of responsibility to answer Americas challenges at home and abroad.

Obama and others paid homage to Lincoln in the form of tributes and references during several of the events, starting with a commemorative train tour from Philadelphia, Pennsylvania, to Washington, D.C. on January 17, 2009. The inaugural events held in Washington from January 18 to 21, 2009, included concerts, a national day of community service on Martin Luther King, Jr. Day, the swearing-in ceremony, luncheon and parade, inaugural balls, and the interfaith inaugural prayer service. The presidential oath as administered to Obama during his swearing-in ceremony on January 20 strayed slightly from the oath of office prescribed in the United States Constitution, which led to its re‑administration the next day.

In addition to a larger than usual celebrity attendance, the Presidential Inaugural Committee increased its outreach to ordinary citizens to encourage greater participation in inaugural events compared with participation in recent past inaugurations. For the first time, the committee opened the entire length of the National Mall as the public viewing area for the swearing-in ceremony,