Savaiʻi is the largest and highest island both in Samoa and in the Samoan Islands chain. The island is also the sixth largest in Polynesia, behind the three main islands of New Zealand and the Hawaiian Islands of Hawaii and Maui. While it is larger than the second main island, Upolu, it is significantly less populated.

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 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.