Nauru (English /nɑːˈuːruː/ nah-oo-roo), officially the Republic of Nauru and formerly known as Pleasant Island, is an island country in Micronesia in the South Pacific. Its nearest neighbour is Banaba Island in Kiribati, 300 kilometres (186 mi) to the east. Nauru is the world's smallest republic, covering just 21 square kilometres (8.1 sq mi). With just over 9,265 residents, it is the second least-populated country after Vatican City.

Settled by Micronesian and Polynesian people, Nauru was annexed and claimed as a colony by the German Empire in the late 19th century. After World War I, Nauru became a League of Nations mandate administered by Australia, New Zealand, and the United Kingdom. During World War II, Nauru was occupied by Japanese troops, who were bypassed by the Allied advance across the Pacific. After the war ended, it entered into trusteeship again. Nauru gained its independence in 1968.

Throughout the first half of the 20th century, Nauru was a "rentier state". Nauru is a phosphate rock island, with deposits close to the surface, which allow for simple strip mining operations. This island was a major exporter of phosphate starting in 1907, when the Pacific Phosphate Company began mining there, through the formation of the British Phosphate Commission in 1919, and continuing after independence. This gave Nauru back full control of its minerals under the Nauru Phosphate Corporation, until the deposits ran out during the 1980s. For this reason, Nauru briefly boasted the highest per-capita income enjoyed by any sovereign state in the world during the late 1960s and early 1970s.

When the phosphate reserves were exhausted, and the environment had been seriously harmed by mining, the trust that had been established to manage the island's wealth diminished in value. To earn income, Nauru briefly became a tax haven and illegal money laundering centre. From 2001 to 2008, it accepted aid from the Australian Government in exchange for housing a Nauru detention centre that held and assessed the refugee claims of asylum seekers who had arrived unauthorised in Australia.

The island has one airport, Nauru International Airport. From January to September 2006, Nauru became partially isolated from the outside world when Air Nauru, the airline which serviced the island, ceased operations in December 2005 and left the island accessible only by ship. The airline was subsequently able to restart operations in October 2006 under the name Our Airline with monetary aid from the Republic of China (Taiwan).

Nauru was first inhabited by Micronesian and Polynesian people at least 3,000 years ago. There were traditionally 12 clans or tribes on Nauru, which are represented in the 12-pointed star in the flag of the country. Nauruans traced their descent matrilineally. Nauruans practiced aquaculture – they caught juvenile ibija fish, acclimatised them to fresh water, and raised them in the Buada Lagoon, providing an additional and more reliable source of food. The other locally grown components of their diet included coconuts and pandanus fruit.

The British sea captain John Fearn, a whale hunter, became the first Westerner to visit this island in 1798, and he named it "Pleasant Island". From around 1830, Nauruans had contact with Europeans from whaling ships and traders who replenished their supplies (such as fresh water) at Nauru. Around this time, deserters from the ships began to live on the island. The islanders traded food for alcoholic palm wine and firearms. The firearms were used during the 10-year Nauruan Tribal War that began in 1878, and by 1888 had resulted in a reduction of the population of Nauru from 1,400 to 900 people.

Nauru was annexed by Germany in 1888 and incorporated into Germany's Marshall Island Protectorate. The Germans called the island Nawodo or Onawero. The arrival of the Germans ended the war, and social changes brought about by the war established kings as rulers of the island. The most widely known of these was King Auweyida. Christian missionaries from the Gilbert Islands arrived in 1888. The Germans ruled Nauru for almost three decades. Robert Rasch, a German trader who married a native woman, was the first administrator, appointed in 1890.

Phosphate was discovered on Nauru in 1900 by the prospector Albert Ellis. The Pacific Phosphate Company started to exploit the reserves in 1906 by agreement with Germany. The company exported its first shipment in 1907. In 1914, following the outbreak of World War I, Nauru was captured by Australian troops. Australia, New Zealand and the United Kingdom signed the Nauru Island Agreement in 1919, creating a board known as the British Phosphate Commission (BPC). This took over the rights to phosphate mining. According to the Commonwealth Bureau of Census and Statistics (now the Australian Bureau of Statistics), "In common with other natives, the islanders are very susceptible to tuberculosis and influenza, and in 1921 an influenza epidemic caused the deaths of 230 islanders." In 1923, the League of Nations gave Australia a trustee mandate over Nauru, with the United Kingdom and New Zealand as co-trustees. On 6 and 7 December 1940, the German auxiliary cruisers Komet and Orion sank four supply ships in the vicinity of Nauru. On the next day, Komet shelled Nauru's phosphate mining areas, oil storage depots, and the shiploading cantilever.

Japanese troops occupied Nauru on 26 August 1942. The Japanese troops built an airfield on Nauru which was bombed for the first time on 25 March 1943, preventing food supplies from being flown to Nauru. The Japanese deported 1,200 Nauruans to work as labourers in the Chuuk islands. Nauru, which had been bypassed and left to "wither on the vine" by American forces, was finally set free from the Japanese on 13 September 1945, when Captain Hisayaki Soeda, the commander of all the Japanese troops on Nauru, surrendered the island to the Australian Army and the Royal Australian Navy. This surrender was accepted by Brigadier J. R. Stevenson, who represented Lieutenant General Vernon Sturdee, the commander of the First Australian Army, on board the warship HMAS Diamantina. Arrangements were made to repatriate from Chuuk the 737 Nauruans who survived Japanese captivity there. They were returned to Nauru by the BPC ship Trienza in January 1946. In 1947, a trusteeship was established by the United Nations, and Australia, New Zealand, and the United Kingdom became the U.N. trustees of the island.

Nauru became self-governing in January 1966, and following a two-year constitutional convention, it became independent in 1968, led by founding president Hammer DeRoburt. In 1967, the people of Nauru purchased the assets of the British Phosphate Commissioners, and in June 1970, control passed to the locally owned Nauru Phosphate Corporation. One of the ships commissioned to ship the natural resources of Nauru was the Eigamoiya, built by the Henry Robb shipyard at Leith in Scotland.

Income from the mining of phosphate gave Nauruans one of the highest living standards in the Pacific and the world.

In 1989, Nauru took legal actions against Australia in the International Court of Justice over Australia's actions during its administration of Nauru. In particular, Nauru made a legal complaint against Australia's failure to remedy the environmental damage caused by phosphate mining. Certain Phosphate Lands: Nauru v. Australia led to an out-of-court settlement to rehabilitate the mined-out areas of Nauru.

Nauruans descended from Polynesian and Micronesian seafarers who believed in a female deity, Eijebong, and a spirit land, an island called Buitani. Two of the 12 original tribal groups became extinct in the 20th century. Angam Day, held on 26 October, celebrates the recovery of the Nauruan population after the two World Wars, which together reduced the indigenous population to fewer than 1500. The displacement of the indigenous culture by colonial and contemporary, western influences is significant. Few of the old customs have been preserved, but some forms of traditional music, arts and crafts, and fishing are still practiced.

There are no daily news publications on Nauru, although there is one fortnightly publication, "Mwinen Ko", meaning 'let's talk about it'. There is a state-owned television station, Nauru Television (NTV), which broadcasts programmes from New Zealand and Australia, and there is a state-owned non-commercial radio station, Radio Nauru, which carries programs from Radio Australia and the BBC.

Australian rules football is the most popular sport in Nauru. There is a football league with seven teams. All games are played at the Linkbelt Oval, one of only two stadiums in Nauru. Other sports popular in Nauru include volleyball, netball, weightlifting, fishing and tennis. Nauru participates in the Commonwealth Games and the Summer Olympic Games, where team members have been somewhat successful in weightlifting. Marcus Stephen has been a medallist, and he was elected to Parliament in 2003, and was elected as President of Nauru in 2007.

A traditional activity is catching noddy terns when they return from foraging at sea. At sunset, men stand on the beach ready to throw their lassos at the incoming birds. The Nauruan lasso is supple rope with a weight at the end. When a bird approaches, the lasso is thrown up, hits or drapes itself over the bird, which falls to the ground. The noddy is then killed, plucked, cleaned, cooked, and eaten.

Nauru is a 21 square kilometres (8 sq mi), oval-shaped island in the southwestern Pacific Ocean, 42 kilometres (26 mi) south of the Equator. The island is surrounded by a coral reef, which is exposed at low tide and dotted with pinnacles. The reef is bounded seaward by deep water, and on the inside by a sandy beach. The presence of the reef has prevented the establishment of a seaport, although 16 channels in reef allow small boats access to the island. A 150 to 300 metre (about 500 to 1,000 ft.) wide fertile coastal strip lies inland from the beach.

Coral cliffs surround Nauru's central plateau, which is known as "Topside". The highest point of the plateau, called the Command Ridge, is 71 metres above sea level. The only fertile areas on Nauru are the narrow coastal belt, where coconut palms flourish. The land surrounding Buada Lagoon supports bananas, pineapples, vegetables, pandanus trees, and indigenous hardwoods such as the tomano tree. The population of Nauru is concentrated in the coastal belt and around Buada Lagoon.

Nauru was one of three great phosphate rock islands in the Pacific Ocean (the others were Banaba (Ocean Island) in Kiribati and Makatea in French Polynesia). However, the phosphate reserves on Nauru are depleted for all practical purposes. Phosphate mining in the central plateau has left a barren terrain of jagged limestone pinnacles up to 15 metres (49 ft) high. A century of mining has stripped and devastated about 80% of the land area. Mining has also affected the surrounding Exclusive Economic Zone, with 40% of marine life estimated to have been killed by silt and phosphate runoff.

There are limited natural fresh water resources on Nauru. Rooftop storage tanks collect rainwater, but the islanders are mostly dependent on three desalination plants housed at Nauru's Utilities Agency. Nauru's climate is hot and very humid year-round – because of the proximity of the island to the Equator and the ocean. Nauru is hit by monsoon rains between November and February. Annual rainfall is highly variable and is influenced by the El Niño-Southern Oscillation, with several significant recorded droughts.

The temperature on Nauru ranges between 26 and 35° Celsius (79 to 95 °Fahrenheit) during the day and between 25 and 28° Celsius (77 to 82 °F.) at night. As an island country, Nauru is quite vulnerable to climate change and sea level change, but to what degree is difficult to predict. At least 80% of the land of Nauru is well-elevated, but this area will be uninhabitable until the phosphate mining rehabilitation program is implemented. Also, the agricultural area of Nauru is quite close to the seashore.

There are only about 60 recorded vascular plant species native to the island, none of which are endemic. Coconut farming, mining, and introduced species have caused serious disturbance to the native vegetation. There are no native land mammals, but there are native birds, including the endemic Nauru Reed Warbler, insects, and land crabs. The Polynesian rat, cats, dogs, pigs, and chickens have been introduced to Nauru from ships, either accidentally or on purpose.