Rarotonga is the most populous island in a group of 15 islands known as the Cook Islands, with about 8,500 residents.

The island is surrounded by a lagoon, which sometimes extends several hundred metres to the reef, which then slopes or drops to deep water. The reef fronts the shore to the north of the island, making the lagoon there unsuitable for swimming and watersports, but to the south east around Muri, the wide, deeper lagoon is popular with tourists because of the suitability of the lagoon for swimming, sailing and boating. Aroa on the south west is the top snorkelling spot. Agricultural terraces, flats, and swamps surround the central mountain area.

The interior of the island is dominated by eroded volcanic peaks cloaked in dense vegetation. Sealed and unsealed roads allow access to valleys but the interior of the island remains largely unpopulated due to forbidding terrain and lack of infrastructure.

A large tract of land has been set aside in the south as the Takitumu Conservation Area to protect the islands' native birds and plants, especially the Endangered Rarotonga Flycatcher, Kakerori.