Rustam Kasimdzhanov[a] (born 5 December 1979) is an Uzbek chess grandmaster and former FIDE World Champion (2004-05).

In addition to his tournament play, Kasimdzhanov was a longtime second to Viswanathan Anand, including during the 2008, 2010 and 2012 World Championship matches.

In the FIDE World Chess Championship 2004 in Tripoli, Libya, Kasimdzhanov unexpectedly made his way through to the final, winning mini-matches against Alejandro Ramírez, Ehsan Ghaem Maghami, Vasyl Ivanchuk, Zoltán Almási, Alexander Grischuk and Veselin Topalov to meet Michael Adams to play for the title and the right to face world number one Garry Kasparov in a match.

On June 23, 2005, in the ABC Times Square studios, the AI Accoona Toolbar driven by a Fritz 9 prototype engine, drew against him.

[5] In 2015 he won the Highlander Cup, a rapid knockout tournament, at the Global Chess Festival, that took place in Budapest and was organized by Judit Polgár.