Roman Catholicism in the United States is part of the worldwide Roman Catholic Church, the Christian Church in full communion with the Pope, currently Pope Benedict XVI. Catholicism arrived in what is now the United States during the earliest days of the European colonization of the Americas. At the time the country was founded only a small fraction of the population were Catholics, but the faith has grown dramatically over the country's history and it is now the largest minority profession of faith in the United States today. With over 67 million registered residents professing the faith in 2008, the United States has the fourth largest Catholic population in the world after Brazil, Mexico, and the Philippines, respectively.

The 2008 Yearbook of American and Canadian Churches, a statistical listing of major religious bodies published by National Council of Churches, reports 67,515,016 registered members of the Roman Catholic Church. The next largest Christian group is a Protestant denomination, the Southern Baptist Convention, which reports only 16,306,246 members.

The Church's leadership body in the United States is the U. S. Conference of Catholic Bishops, made up of the hierarchy of bishops and archbishops of the United States and the U.S. Virgin Islands, although each bishop is independent in his own diocese, answerable only to the Pope.

No primate for Catholics exists in the United States. The Archdiocese of Baltimore, the first diocese established in the country in 1789 with John Carroll as its head, received Prerogative of Place in the 1850s, which confers to its archbishop a subset of the leadership responsibilities granted to primates in other countries. Bishop Carroll's family was very well connected. His cousin, Charles Carroll of Carrollton, one of the richest men in America, was the only Catholic signer of the Declaration of Independance and first United States senator from Maryland. In 1774, the colonial government commissioned John Carroll, Benjamin Franklin, Samuel Chase, and his cousin, Charles Carroll of Carrollton, to seek aid from British Canada (which at the time was predominately French Catholic). The bishop's younger brother, Daniel Carroll, a good friend of James Madison, was one of only five men to sign both the Articles of Confederation and the Constitution of the United States.