Monaco /ˈmɒnəkoʊ/, officially the Principality of Monaco (French: Principauté de Monaco; Monégasque: Principatu de Múnegu; Italian: Principato di Monaco; Occitan: Principat de Mónegue), is a sovereign city state on the French Riviera. It is bordered on three sides by its neighbour, France, and its centre is about 16 km (9.9 mi) from Italy. Its area is 1.98 km (0.76 sq mi) with a population of 35,986 as of 2011 and is the most densely populated country in the world. Monaco boasts the world's highest GDP nominal per capita at $151,630. Monaco also has the world's highest life expectancy at almost 90 years (CIA estimate, 2011), and the lowest unemployment rate at 0%, with about 40,000 workers who commute from France and Italy each day. After a recent expansion of Port Hercule, Monaco's total area is 2.05 km (0.79 sq mi), with new plans to extend the district of Fontvieille, with land reclaimed from the Mediterranean Sea.

Monaco is a principality governed under a form of constitutional monarchy, with Prince Albert II as head of state. The House of Grimaldi has ruled Monaco, with brief interruptions, since 1297. The state's sovereignty was officially recognized by the Franco-Monegasque Treaty of 1861. Despite Monaco being independent and pursuing its own foreign policy course, its national defence is the responsibility of France.

Citizens of Monaco are called Monacans, while Monegasque is the proper term for describing someone who was born in Monaco.

Monaco's name comes from the 6th century BC nearby Phocaean Greek colony. Referred to the Ligurians as Monoikos, from the Greek "μόνοικος", "single house", from "μόνος" (monos) "alone, single" + "οἶκος" (oikos) "house", which bears the sense of a people either settled in a "single habitation" or of "living apart" from others. According to an ancient myth, Hercules passed through the Monaco area and turned away the previous gods. As a result, a temple was constructed there, the temple of Hercules Monoikos. Because the only temple of this area was the "House" of Hercules, the city was called Monoikos.

Following a land grant from Emperor Henry VI in 1191, Monaco was re-founded in 1215 as a colony of Genoa. Monaco was first ruled by a member of the House of Grimaldi in 1297, when Francesco Grimaldi ("Il Malizia", translated from Italian either as "The Malicious One" or "The Cunning One") and his men captured the fortress protecting the Rock of Monaco while he was dressed as a Franciscan monk – a Monaco in Italian, although this is a coincidence as the area was already known by this name. Francesco, however, was chased off only a few years afterwards by the Genovese forces, and the struggle over "the Rock" continued for another century.

In 1419, the Grimaldis purchased Monaco from the crown of Aragon and became the official and undisputed rulers of "the Rock of Monaco", and it was in 1612 Honore II began to style himself "Prince" of Monaco. In the 1630s, Honore II sought French protection against the Spanish forces and was eventually, in 1642, received in the court of Louis XIII as "Duc et Pair Etranger". The princes of Monaco thus became a vassal of the French kings while at the same time remained a sovereign prince. As the successive princes and their families spent most of their lives in Paris, and through marriages with French nobilities, the House of Grimaldi, Italian in origin, became thoroughly French in character. The principality continued its existence as a protectorate of France until the Great Revolution.

In 1793, French Revolutionary forces captured Monaco and it remained under direct French control until 1814 when the Bourbons returned to the throne. The principality was re-established that year, only to be designated a protectorate of the Kingdom of Sardinia by the Congress of Vienna in 1815. Monaco remained in this position until 1860 when, by the Treaty of Turin, the Sardinian forces pulled out of the principality and the surrounding county of Nice (as well as Savoy) was ceded to France. Monaco became a French protectorate once again. Prior to this time there was unrest in Menton and Roquebrune where the townspeople had been weary of heavy taxation by the Grimaldis, and declared independence hoping for annexation by Sardinia. France protested. The unrest continued until Charles III gave up his claim to the two mainland towns (some 95% of the principality) that the Grimaldis ruled for over 500 years. They were ceded to France in return for 4,100,000 francs. The transfer and Monaco's sovereignty was recognised by the Franco-Monegasque Treaty of 1861. In 1869, the principality stopped collecting income tax from its residents; indulgence the Grimaldis could afford to entertain thanks solely to extraordinary success of the casino. This made Monaco not only the playground for the rich, but the place to live.

20th century

Until the Monegasque Revolution of 1910 forced the adoption of the 1911 constitution, the princes of Monaco were absolute rulers. The long over-due constitution, however, barely reduced the autocratic rule by the Grimaldis and Albert I soon suspended it. In July 1918, the Franco-Monegasque Treaty was signed providing for limited French protection over Monaco. The treaty, endorsed in 1919 by the Treaty of Versailles, established that Monegasque international policy would be aligned with French political, military, and economic interests, and resolved the Monaco Succession Crisis.

In 1943, the Italian army invaded and occupied Monaco, setting up a Fascist administration. Shortly thereafter, following Mussolini's collapse in Italy, the Nazi German Wehrmacht occupied Monaco and began the deportation of the Jewish population. René Blum (Paris, 13 March 1878 – Auschwitz, 30 April 1943), the prominent French Jew who founded the Ballet de l'Opera in Monte Carlo, was arrested in his Paris home and held in the Drancy deportation camp outside Paris, whence he was then transported to the Auschwitz concentration camp, where he was killed. Blum's colleague Raoul Gunsbourg, the director of the Opéra de Monte-Carlo, was helped by the French Resistance to escape arrest and flee to Switzerland.

Rainier III, who ruled until 2005, acceded to the throne following the death of his grandfather, Prince Louis II, in 1949. On 19 April 1956, Prince Rainier married the American actress Grace Kelly; the event was widely televised and covered in the popular press, focusing the world's attention on the tiny principality.

A 1962 amendment to the constitution abolished capital punishment, provided for women's suffrage, and established a Supreme Court of Monaco to guarantee fundamental liberties. In 1993, the Principality of Monaco became a member of the UN, with full voting rights. In 2002, a new treaty between France and Monaco specified that, should there be no heirs to carry on the Grimaldi dynasty, the principality would still remain an independent nation rather than revert to France. Monaco's military defence, however, is still the responsibility of France.

On 31 March 2005, Prince Rainier III, too ill to exercise his duties, relinquished them to his only son and heir, Prince Albert Alexandre Louis. Prince Rainier died on 6 April 2005, after a reign of 56 years, and his son, by Princess Grace, succeeded him as Albert II, Sovereign Prince of Monaco.

Following a period of official mourning, Prince Albert II formally assumed the princely crown on 12 July 2005, in a celebration that began with a solemn Mass at Saint Nicholas Cathedral, where his father had been buried three months earlier. His accession to the Monegasque throne was a two-step event, with a further ceremony, drawing heads of state for an elaborate levée, held on 19 November 2005 at the historic Prince's Palace in Monaco-Ville.

With a total area of 2.05 square kilometres (0.79 sq mi), a land border of 5.469 kilometres (3.4 mi) and a coast measuring 3.829 kilometres (2.4 mi) the Principality of Monaco is the second-smallest independent state in the world, after the Vatican City. It lies on the coast of the Mediterranean Sea, 18 kilometres (11 mi) east of Nice, and is surrounded on three sides by France and on the fourth by the sea into which its maritime claims extend to 22.2 kilometres (13.8 mi). Its highest point is 163 metres (535 ft) above sea level, on the southern slopes of Mont Agel whose 1,109 m (3,638 ft) peak is in France. The country has no natural resources.

Monaco has a warm-summer Mediterranean climate (Köppen climate classification: Csa), which is influenced by the oceanic climate and the humid subtropical climate.

As a result, it has warm, dry summers and mild, rainy winters. Cool and rainy interludes can interrupt the dry summer season, the average length of which is also shorter. Summer afternoons are infrequently hot (indeed, temperatures > 30 °C /86 °F are rare) as the atmosphere is tempered by constant sea breezes. On the other hand, the nights are very mild, this being due to the fairly high temperature of the sea in summer. Generally, temperatures do not drop below 20 °C in this season. In winter, frosts and snowfalls are extremely rare, generally occurring once or twice every ten years.