Between the 1790s and the 1990s, the Irish American population grew from some 500,000 to nearly 40 million. Part of this growth was due to immigration, especially in the years of the Great Irish Famine, though significant emigration from Ireland both preceded and followed the famine decade of 1846–1855. For much of this 200-year period, Irish-born men and women and their descendants were heavily concentrated in working-class occupations and urban communities. Especially in the years around the opening of the 20th century, Irish Catholic immigrants and their descendants put a distinctive stamp on both the American labor movement and urban working-class culture and politics as a whole. Their outsized influence diminished somewhat over the course of the 20th century, but the American Irish continued to occupy key leadership positions in the U.S. labor movement, the Democratic Party, and the American Catholic Church, even as the working-class members or constituents of these institutions became increasingly ethnically diverse. The experience of Irish American working people thus constitutes an important dimension of a larger story—that of the American working class as a whole.