Upolu is an island in Samoa, formed by a massive basaltic shield volcano which rises from the seafloor of the western Pacific Ocean. The island is 75 kilometres long and 1,125 square kilometres in area, making it the second largest of the Samoan Islands by area. With approximately 145,000 inhabitants, it is by far the most populous of the Samoan Islands. Upolu is situated to the southeast of Savai'i, the "big island". Apia, the capital, is in the middle of the north coast, and Faleolo International Airport is at the western end of the island. The island has not had any historically recorded eruptions, although there is evidence of three lava flows, dating back only to between a few hundred and a few thousand years ago.
In the Samoan branch of Polynesian mythology, Upolu was the first woman on the island.
James Michner based his character Bloody Mary in Tales from the South Pacific on the owner of Aggie Grey's Hotel on the south end of the island. She was still running the hotel in 1960. A branch was later opened in Apia overlooking the harbor.