Abstract: Land–sea thermal contrast is the fundamental driving force for the onset and evolution of the Asian summer monsoon. The Tibetan Plateau–Indian Ocean thermal contrast is a crucial factor influencing South Asian monsoon activity. This article reviews and summarizes relevant research results on the effects of the Tibetan Plateau–Indian Ocean thermal contrast on South Asian monsoon activity on various time scales, including subseasonal, seasonal, interannual, and interdecadal scales. On the subseasonal scale, the main focus is on the influence of thermal contrast on the onset of the South Asian monsoon. On the interannual scale, emphasis is placed on the indicative significance of the thermal contrast concerning the interannual variation in monsoon intensity. On the interdecadal scale, the interdecadal variations in the relationship between the thermal contrast and South Asian monsoon precipitation are examined. This article discusses some issues that require further research in this field.