In the last decade of the 19th Century, Ellis Island, in New York Harbor, was designated as the main arrival port for immigrants. The facility stayed in service until the 1950s, and 12 million immigrants passed through its entrance halls. Ellis Island was not the only port where immigrants entered the United States, but in the popular mind it has become synonymous with immigration to America.
At the official web site for Ellis Island visitors can learn about the history of American immigration and can even look up their own ancestors. A successful search will result in the researcher being able to view a facsimile of a ship's manifest showing the name of an ancestor. The site, in short, is a genealogist's dream.