Rustam Kasimdzhanov (Uzbek: Rustam Qosimjonov; Russian: ?????? ???????????; born 5 December 1979) is an Uzbekistani chess grandmaster and former FIDE World Champion (2004-05).
He was Asian champion in 1998.
Long-time second to Viswanathan Anand – helping him in the 2008, 2010 and 2012 World Championship matches – he has also trained with Sergey Karjakin and Fabiano Caruana.