Severe flooding occurred during the 2011 monsoon season in Thailand.Flooding persisted in some areas until mid-January 2012, and resulted in a total of 815 deaths (with 3 missing) and 13.6 million people affected. Sixty-five of Thailand's 77 provinces were declared flood disaster zones, and over 20,000 square kilometres (7,700 sq mi) of farmland was damaged. The disaster has been described as "the worst flooding yet in terms of the amount of water and people affected."

The World Bank has estimated 1,425 billion baht (US$ 45.7 Bn) in economic damages and losses due to flooding, as of 1 December 2011.