Long (Plio-Pleistocene) summer monsoon records have now been produced from the Arabian Sea, South China Sea and Chinese Loess Plateau, representing both the Indian and East Asian monsoon sub-systems.All records have all been placed on the global marine benthic oxygen isotope time-scale (LR04).These Indian and East Asian records are synthesized to evaluate the timing of maximum summer monsoon circulation relative to external insolation forcing at the Earth-orbital obliquity and precession bands and to infer from these relationships, the primary internal and external mechanisms driving changes in monsoon strength at orbital time scales.Summer-monsoon records from all three locations have similar phase responses at the obliquity and precession bands indicating that the Indian and East Asian systems are tightly coupled and driven by common forcing mechanisms throughout the past 2.7 Ma.