Niʻihau (Hawaiian: [ˈniʔiˈhɐw]), anglicized as Niihau (/ˈniː(i)haʊ/ NEE-(ee-)how), is the westernmost main and seventh largest island in Hawaii.

The island is designated as critical habitat for Brighamia insignis, an endemic and endangered species of Hawaiian lobelioid.

The island, known as "the Forbidden Isle", is off-limits to all outsiders except the Robinson family and their relatives, U.S. Navy personnel, government officials, and invited guests.

[9] The island is relatively arid because it lies in the rain shadow of Kauaʻi and lacks the elevation needed to catch significant amounts of trade wind rainfall.

Niʻihau, therefore, depends on winter Kona storms for its rain, when more northerly weather systems intrude into the region.

[10] Historical droughts on Niʻihau have been recorded several times, one in 1792 by Captain James Cook's former junior officer, George Vancouver, who had been told that the people of Niʻihau had abandoned the island because of a severe drought and had moved to Kauaʻi to escape famine.

[11] As an arid island, Niʻihau was barren of trees for centuries – Captain James Cook reported it treeless in 1778.

[13] Island co-owner Keith Robinson, a noted conservationist, preserved and documented many of Niʻihau's natural plant resources.

The critically endangered Hawaiian monk seal (Monachus schauinslandi) is found in high numbers on Niʻihau's shores.

They have been relocated to the main Hawaiian island chain by NOAA fisheries over the past thirty years, and some have found homes on Niʻihau.

[13][15][16] Big game herds, imported from stock on Molokaʻi Ranch in recent years, roam Niʻihau's forests and flatlands.

[17][18] Kāʻeokūlani was a ruler of northern Niʻihau who unified the island after defeating his rival, a chief named Kawaihoa.

Kāʻeo married the Queen Kamakahelei, and a future king of Niʻihau and Kauaʻi named Kaumualiʻi was born in 1790.

[20] Two attempts to conquer those islands had failed, and Kamehameha lost many men: bodies covered the beaches on Kauaʻi's eastern shores.

[21] Finally, in 1810, Kamehameha amassed a great fleet, and Kaumualiʻi, the last independent aliʻi, surrendered rather than risk further bloodshed.

[22] This era marked the end of the art of Hawaiian mat-weaving made famous by the people of Niʻihau.

The mats were valued by aliʻi and foreign visitors alike, but by the end of the 19th century, Hawaiians had stopped weaving makaloa due to changes in population, culture, economics, and the environment.

[29] The island of Niʻihau was considered as a possible location for the United Nations headquarters in 1944 by Franklin D. Roosevelt, who had visited Hawaii in 1934.

The Niʻihau dialect differs from modern standard Hawaiian in that, for example, [t] and [ɾ] are the most common realizations of the phonemes /k/ and /l/, respectively.

[40] Oral tradition maintains that the Niʻihau dialect is closer to the Hawaiian register spoken during the time of contact with Europeans; there is linguistic evidence to support this claim, such as the pronunciation of k as /t/.

[42] Niʻihau is subject to regular droughts that occasionally force the population to evacuate to Kauaʻi temporarily, until rainfall replenishes their water supply.

Residents commonly also commute to Kauaʻi for work, medical care, or school, and many of them call both islands home.

To avoid a long boat ride, the island's owners maintain an Agusta A109 helicopter for emergencies and for transporting Navy contractors and residents to and from Kauaʻi.

Hawaiian music plays a central role on the island, with a cappella singers making use of only two or three tones and changing rhythms.

The school has a digital recording and video system, which helps to preserve and teach traditional Niʻihau and Hawaiian culture.

The installation brings in millions of dollars a year, and provides the island with a stable economic base without the complexity of tourism or industrial development.

Robinson has declined offers to purchase sand from Niʻihau's beaches, because of adverse environmental effects.

[13] Niʻihau's owners have offered half-day helicopter and beach tours of the island since 1987,[55] although contact with residents is avoided and no accommodation exists.