Extreme weather events, especially heat waves, have become more frequent with global warming. High temperature significantly affects world food security by decreasing crop yield. Rice is intensively planted in tropical and subtropical areas in Asia, where high temperature has become a major factor affecting rice production. Rice is sensitive to high temperature, especially at booting and flowering stages. Rice varieties tolerant of high temperature are rare, and only a few heat-tolerant rice varieties have been identified. High temperature at booting and flowering stages causes sterile pollen, decreased pollen shedding, and poor pollen germination, which finally lead to a yield decrease. Heat-tolerant QTLs have been identified in different studies, but new breeding lines with considerable heat tolerance have not been bred using identified heat-tolerance donors and QTLs. Research on heat-tolerant donor identification, QTL mapping, gene cloning, and large-scale phenotyping technology is important for developing heat-tolerant rice varieties.