Alexandra Konstantinovna Kosteniuk (Russian: Александра Константиновна Костенюк; born April 23, 1984 in Perm, Volga Federal District) is a Russian chess Grandmaster and the current Women's World Chess Champion.

Alexandra learned to play chess at the age of five after being taught by her father. She has a little sister named Oxana, who is a FIDE master level chess player.

In 2001, at the age of 17, she reached the final of the World Women's Chess Championship, but was defeated by Zhu Chen. Three years later, she became European women's champion by winning the tournament in Dresden, Germany. She also won the 2005 Russian Women's Championship, held in Samara, Russia, finishing with a score of +7 =4 -0. In August 2006, she became the first Chess960 (Fischer random) women's world champion after beating Germany's top female player Elisabeth Pähtz 5.5-2.5. She defended that title successfully in 2008 by beating Kateryna Lahno 2.5-1.5. However, her top success so far has been to win the Women's World Chess Championship 2008, beating in the final the young Chinese prodigy Hou Yifan, with a score of 2.5-1.5.

In November 2004, she was awarded the International Grandmaster title, becoming the tenth woman to receive the highest title of the World Chess Federation, FIDE. Before that, she had also obtained the titles of Woman Grandmaster and International Master. She is 11th on the April 2009 FIDE women's Elo rating list with a rating of 2516.

Kosteniuk's mottos have been "chess is cool" and "beauty and intelligence can go together". With these as a backdrop, Kosteniuk has been promoting chess in the capacity of a fashion model and ambassador of chess in order to spark interest in the game around the world.

She is also the host of a popular podcast "Chess is Cool" which informs listeners about Alexandra's life and current chess events.

She is due to defend her title in the Women's World Chess Championship, 2010.

Kosteniuk is married to Swiss-born Diego Garces, who is of Colombian descent, and 25 years older than her. On April 22, 2007 Alexandra gave birth to a daughter, Francesca Maria. Francesca was born 2½ months premature, but after an 8-week stay in the hospital has made a full recovery.

Alexandra and her husband live in Key Biscayne, Florida, a suburb of Miami. Kosteniuk has been compared to Russian tennis knockout (and Miami Beach resident) Anna Kournikova. Kosteniuk debunks the comparison by noting that she has won individual tournaments, a feat the other Russian cannot claim. Alexandra and her husband decided to make South Florida their home because Kosteniuk prefers the weather to Moscow's, and Garces' parents live here. They are also close to the World Chess Hall of Fame in West Kendall, where there is an Alexandra the Great exhibit highlighting Kosteniuk's successes.

Alexandra's website, which is maintained by her husband, covers the chess events she is participating in and offers current information about her.