Greek Americans are Americans of full or partial Greek ancestry. They number at least 1.2 million, of whom 264,066 (22%) over the age of five speak Greek at home.

The United States is home to the largest number of Greeks outside Greece, followed by Cyprus and Australia. Greek Americans have the highest concentrations in New York City, Boston, and Chicago, but have settled in major metropolitan areas across the United States. In 2000, Tarpon Springs, Florida, was home to the largest community of Greek Americans proportionally, at just over 10%.

Within the New York City region, Astoria, Queens contains a vibrant Greek community and an official Greektown. Officially city-designated Greektowns exist in Chicago, Detroit, and Tarpon Springs in the Tampa area. Greek community enclaves have been found in other metropolitan areas, such as in the San Francisco Bay Area, Los Angeles, Philadelphia, and rural areas such as Campbell, Ohio are home to Greek enclaves. There are also strong Greek communities in Boston, the Salt Lake Valley, and in North Carolina, especially Charlotte and Asheville areas.

The first Greek to ever set foot in America was Johan Griego (lit. 'John the Greek'), in 1492. He was a member of Christopher Columbus's first expedition. At least two other Greeks followed soon after; they were brothers who sailed with Columbus in his second (1493) and third (1498) expeditions. Spanish and English historians mention three Greeks who sailed with Ferdinand Magellan in 1520 on his voyage to Patagonia. Their names are listed as: Nikolao, Ioanni, and Mattheo.

Another Greek, Don Doroteo Teodoro, was a sailor who landed in Boca Ciega Bay at the Jungle Prada site in present-day St. Petersburg, Florida with the Narváez expedition in 1528. He was instrumental in building the rafts that the expedition survivors built and sailed from present-day St. Mark's River in Florida until they were shipwrecked near Galveston Island, Texas. Teodoro had been captured by natives as they sailed along the Gulf coast shoreline toward the west, and was never seen again. He was presumably killed by the natives. Don Doroteo Teodoro is regarded as the first Greek to have set foot on soil which is today part of the United States. Pedro de Candia (lit. 'Petros the Cretan', a Greek adventurer and soldier from Crete, is known for being a lieutenant of Francisco Pizarro who conquered the empire of Peru and founded the city of Lima.

When Francis Drake reached Valparaiso, Chile in 1578 he found there a Greek pilot, whose name was Ioannis. loannis acted as Drake's pilot as far as Lima, Peru. Ten years later, Thomas Cavendish met a Greek pilot by the name of Georgio, who knew the waters of Chile. Both of these Greek pilots must have been in the area for many years in order to have sufficient knowledge of the waters to act as pilots for visiting ships.

In 1592, Greek captain Juan de Fuca (original name: Ioannis Fokas or Apostolos Valerianos) sailed up the Pacific coast under the Spanish flag, in search of the fabled Northwest Passage between the Pacific and the Atlantic. He reported discovering a body of water, a strait which today bears his name: the Strait of Juan de Fuca, which today forms part of the Canada–United States border.

There is a report that a Cretan Greek named Konopios operated a coffeehouse in New England in 1652. Records show that a Greek, Michael Dry (Youris), became a naturalized citizen by act of the General Assembly of Maryland in 1725. This makes Dry the first Greek positively known to reside permanently in what is today the United States.