The Washington Nationals' 2009 season was the fifth season for the American baseball franchise of Major League Baseball in the District of Columbia, and the 41st since the original team was started in Montreal, Quebec, Canada. It involved the Nationals attempting to win the National League East after a disappointing 59–102 season the year before.

On July 12, manager Manny Acta was fired and replaced with bench coach Jim Riggleman, though only as an interim manager. Under Acta, the Nationals compiled an MLB worst 26–61 record in 2009 through the All-Star break and a 158–252 record in Acta's three seasons with the Nationals. Riggleman would be named full-time manager in November 2009.

The Nationals finished the year with a 59–103 record, worse than the year before by one loss. For the second straight season, they finished with the worst record in Major League Baseball.

Nationals' third baseman Ryan Zimmerman won a Gold Glove Award as the best defensive third baseman in the National League and a Silver Slugger Award as the best offensive third baseman in the league. It would be the final season the Nationals lost a hundred games for 13 years.

On November 3, 2008, the Nationals traded minor-leaguer Ryan Buchter to the Chicago Cubs for minor-leaguer Matt Avery.^[1] On November 10, 2008, they traded Emilio Bonifacio and minor-leaguers Jake Smolinski and P. J. Dean to the Florida Marlins for Scott Olsen and Josh Willingham.^[2]

For the 2009 season, the Nationals altered their uniforms. The interlocking "DC" was removed from the star-spangled circle and moved to the left sleeve of both the home and away uniforms. It also has removed from the alternate red jersey and replaced with the "curly W" from the team's cap. A new navy alternate jersey with the interlocked "DC" on the left chest in a "stars and stripes" flag pattern, which has also been emulated on the alternate navy cap, which was worn several times in 2009. Finally, in a tribute to the former baseball teams in the District of Columbia, a script writing of the city name replaced the block lettering, emulating the Senators' script of the 1950s and 1960s – though as those teams used "Senators" on both their home and away uniforms, this marks the first time the "curly W" has actually appeared as part of the word "Washington" on an MLB jersey.

The uniforms gained notoriety when on April 17 in a game against the Florida Marlins, the jerseys of Ryan Zimmerman and Adam Dunn read "Natinals" on the front of the jersey instead of "Nationals" for the first three innings of the game.^[3] The Nationals did not catch the error as they only checked the back of the shirts, not the front, but were able to assign to Dunn and Zimmerman the correct jerseys later in the game.^[4] The company who manufactured the jerseys, Majestic Athletic, apologized for the error.

The Nationals′ marketing and advertising theme for the 2009 season was "Natstown," capturing the idea that all Nationals fans at the ballpark, in the community, and in their everyday lives were participating in a single community centered around the team. The marketing campaign urged fans to "Get Your Red On," a reference to wearing the team's colors to show one's team spirit.^[5]

In March 2009, the Nationals introduced a new version of Screech, their bald eagle mascot who wears the home cap and jersey of the team. The original Screech who "hatched" at Robert F. Kennedy Memorial Stadium in 2005 during the third home game in Nationals history and had appeared at the team's home games during its first four seasons in Washington, was chubby, but the new Screech was slim. The Nationals explained that they had redesigned Screech because he had "grown up" and become a "teenager."^[6]

The Nationals held their 2009 spring training in Viera, Florida, with home games played at Space Coast Stadium.

The future for the Nationals seemed to show promise in 2009 with their Gulf Coast League affiliate qualifying for the playoffs. The significance of this to the 2009 Major League team was that it demonstrated that the team was attempting to improve on its performance and had the prospects to do so.