Niihau in the context of Hawaiian lobelioids

The Northwestern Hawaiian Islands, also known as the Leeward Hawaiian Islands, are a series of mostly uninhabited islands and atolls located northwest of Kauai and Niʻihau in the Hawaiian island chain. Politically, these islands are part of Honolulu County in the U.S. state of Hawaii, with the exception of Midway Atoll, though they are generally not included on maps and graphic depictions of the State of Hawaii. Midway Atoll is a territory distinct from the State of Hawaii, and is classified as one of the United States Minor Outlying Islands. The United States Census Bureau designates this area, excluding Midway Atoll, as Census Tract 114.98 of Honolulu County. The total land area of these islands is 3.1075 square miles (8.048 km²). With the exception of Nīhoa, all of the islands lie north of the Tropic of Cancer, making them the only islands in Hawaii situated outside the tropics.

Almost all of the islands are uninhabited, the main exception being Midway Atoll, which maintains a permanent rotating population of U.S. Fish and Wildlife Service staff and other workers. Kure Atoll and Tern Island have a seasonal population of a small team of environmental staff. At least some of the islands were visited by Ancient Hawaiians, with Nīhoa showing evidence of permanent habitation.

Brighamia insignis, commonly known as ʻŌlulu or Alula in Hawaiian, or colloquially as the vulcan palm or cabbage on a stick, is a species of Hawaiian lobelioid in the bellflower family, Campanulaceae. It was native to the islands of Kauaʻi and Niʻihau, but has been extinct in the wild since at least 2020. This short-lived perennial species is a member of a unique endemic Hawaiian genus with only one other species.

Lehua Island is a small, crescent-shaped island in the Hawaiian Islands, 0.7 miles (1.1 km) north of Niʻihau, 18 miles due west of Kauaʻi. This uninhabited, 285-acre (1.15 km) barren islet was one of the first five islands sighted by Captain James Cook in 1778 which he spelled as "Oreehoua".

Lehua Island is a Hawaii State Wildlife Sanctuary. As a restricted sanctuary, all activities are prohibited on the island without a permit. Public access to the island is restricted to areas below the high tide water mark. Lehua provides habitat for at least 16 species of seabirds. A population of European rabbits had lived on the island for many years but were removed in 2005. Polynesian rats, first documented on the island in the 1930s, were declared eradicated in 2021.

Elizabeth McHutcheson Sinclair (26 April 1800 – 16 October 1892) was a Scottish homemaker, farmer, and plantation owner in New Zealand and Hawaii, best known as the matriarch of the Sinclair family that bought the Hawaiian island of Niʻihau in 1864. Born in Glasgow, Scotland, she married Francis Sinclair, a ship's captain. With six children in tow, the family moved to New Zealand. Her husband and eldest son (and much of the family's property) were later lost at sea.

After years of farming, mainly at Pigeon Bay on the Banks Peninsula in the Canterbury region of the South Island, she decided to relocate to Canada. Unhappy with the conditions she found on Vancouver Island, she considered California but instead went to Hawaii where she bought the Hawaiian island of Niʻihau for US$10,000 (equivalent to about $201,000 in 2024). This would have been roughly 530 troy ounces of gold, which in 2024 would be worth about $660,000. She later bought additional lands at Hanapepe and Makaweli on the island of Kauaʻi. Her descendants, the Robinson family, continue to own and maintain the island of Ni'ihau.

Aubrey Robinson (October 17, 1853 – July 7, 1936) was an owner of the Hawaiian island of Niihau, a sugarcane plantation developer, and a rancher.