Irish Americans are citizens of the United States who can trace their ancestry to Ireland. A total of 36,278,332 Americans—estimated at 11.9% of the total population—reported Irish ancestry in the 2008 American Community Survey conducted by the U.S. Census Bureau. Roughly another 3.5 million (or about another 1.2% of Americans) identified more specifically with Scotch-Irish ancestry. The Irish diaspora population in the United States is roughly 6 times the modern population of Ireland.

The only self-reported ancestral group larger than Irish Americans is German Americans. The Irish are widely dispersed in terms of geography, and demographics. Irish American political leaders have played a major role in local and national politics since before the American Revolutionary War: eight Irish Americans signed the United States Declaration of Independence, and 22 American Presidents, from Andrew Jackson to Barack Obama, have been at least partly of Irish ancestry. (See "American Presidents with Irish ancestry" below.)

The Irish people (Irish: Muintir na hÉireann or na hÉireannaigh; Ulster-Scots: Airisch or Airish fowk) are an ethnic group who originate in Ireland, an island in northwestern Europe. Ireland has been populated for around 9,000 years (according to archaeological studies, see Prehistoric Ireland). The Irish people's earliest ancestors are recorded in legends – they are claimed to be descended from groups such as the Nemedians, Fomorians, Fir Bolg, Tuatha Dé Danann and the Milesians.Lebor Gabála Érenn, a book of Irish mythology tells that Tuatha Dé Dananns were Scythian descendants.

The main groups that interacted with the Irish in the Middle Ages include the Picts, Scots, and the Vikings. Due to this contact, Icelanders are noted for having some Irish descent. The Anglo-Norman invasion of the High Middle Ages, the English plantations and the subsequent English rule of the country introduced the Normans and Flemish into Ireland. Welsh, Picts, Bretons, and small parties of Gauls and even Anglo-Saxons are known in Ireland from much earlier times.

Dylan Moran (born 3 November 1971) is an Irish stand-up comedian, writer, actor and filmmaker. He is best known for his sardonic observational comedy, the UK television sitcom Black Books (which he co-wrote and starred in), and his work with Simon Pegg in Shaun of the Dead and Run Fatboy Run. Moran also appeared as one of the two lead characters in the Irish black comedy titled A Film with Me in It in 2008. He is a regular performer at national and international comedy festivals including the Edinburgh Festival Fringe, Just for Laughs Montreal Comedy Festival, the Melbourne International Comedy Festival and the Kilkenny Comedy Festival. In 2007 he was voted the 17th greatest stand-up comic on Channel 4's 100 Greatest Stand-Ups and again in the updated 2010 list as the 14th greatest stand-up comic. In 2012, he became the first professional English-speaking comedian ever to perform in Russia, after two sold-out shows in neighboring Estonia, with his routine referencing Russia's new law banning "homosexual propaganda" and jailed oil tycoon Mikhail Khodorkovsky.

English Americans (occasionally known as Anglo-Americans, although this may have a wider linguistic meaning) are citizens of the United States whose ancestry originates wholly or partly in England.

According to American Community Survey in 2010 data, Americans reporting English ancestry made up an estimated 9.0% of the total U.S. population, and form the third largest European ancestry group after German Americans and Irish Americans. However, demographers regard this as an undercount, as the index of inconsistency is high, and many, if not most, people from English stock have a tendency to identify simply as Americans or, if of mixed European ancestry, nominate a more recent and differentiated ethnic group. Throughout the nineteenth century, England was the largest investor in American land development, railroads, mining, cattle ranching, and heavy industry. Perhaps because English settlers gained easy acceptance, they founded few organizations dedicated to preserving the traditions of their homeland.