An overview is presented on the reports available so far on sweet potato, Ipomoea batatas, cultivated widely in Polynesia in the pre-Columbian era, with reference to possible ways and presumptive dates of transfer from the Americas to Polynesia, such as (1) Polynesian navigators' travel to Peru, (2) Peruvian fishermen's drift westward, (3) vessel drift, (4) seed drift, (5) root-tuber drift, and (6) transport by birds. The author supports the case (1) as most plausible. Ganshu or Ganchu described in the old Chinese herbal books is identified as Dioscorea esculenta. An introduction of the tuber to China and Japan is briefly mentioned.