The emigration/immigration process, often documented by both the country of departure and the country of arrival, generated many records that can be extremely helpful to genealogists, and the number of records increases the more recent the immigration.

Upon departure, the emigrant might have obtained a letter of manumission (freeing him or her from the head of the house for whom the emigrant worked), a sale of property, a letter of recommendation from a local church, a permit to emigrate (after having paid all bills and settled personal affairs), or, in more recent years, a passport. Emigrants who were too poor to pay their passage might also have signed a contract indenturing themselves to work for someone who paid their cost. A family may have stopped for a while at a port of call and thus may be found in the local church records. Upon clearing customs at each departure point, passenger lists were usually compiled and filed with local authorities by the captain.

Upon arrival in the new country, another passenger list was made by the officials in the country of arrival, often from information about themselves and their families provided orally by the immigrants, and sometimes by having them sign their names. Immigrants who had medical problems might be found in the records of the "pest" hospitals and newspaper hospital reports. Diaries or journals written by passengers on the ship might name fellow passengers and describe mutual experiences. Some early immigrants were asked to sign an Oath of Allegiance to the new country, renouncing their ties with the old monarchy. Later aliens usually made a declaration of intention to file for naturalization within three to ten years of their arrival (the laws governing when the immigrant could make the declaration changed several times over the years). The aliens petitioned for and received a certificate of naturalization tow or three years after declaring intent. While each of these records can provide valuable information, the arrival records are especially important because they are more accessible and the later records may provide a point of origin in the old country (essential to continued research); also, many records are indexed.

Many good printed regional indexes of early immigrants have been published, especially for arrivals before about 1700. These indexes can be located in the catalog at the Family History Library (FHL) operated by The Church of Jesus Christ of Latter-day Saints in Salt Lake City, Utah, or in the card catalog of large libraries under the location (often a state) involved. The indexes for Rhode Island, Connecticut, Maine, New Hampshire, Pennsylvania Germans, and the first settlers in New England are among the most notable of the printed indexes. Some excellent books about particular emigrant groups are: The Famine Immigrants Series, for emigrants from Ireland between 1846 and 1851; the Directory of Scots Banished to the American Plantations, for Scots who emigrated between 1650 and 1775; the Germans to America Series, for certain German emigrants from 1850 to 1872; the Wuerttemberg Emigration Index, for Germans who filed to emigrate from Wuerttemberg between about 1790 and 1900; Italians to America, for Italians who arrive between 1880 and 1899; Luxembourgers in the New World, for emigrants from Luxembourg who arrived before 1889, including where the settled; Dutch Immigrants in United States Ship Passenger Manifests, for Dutch emigrants who arrived between 1820 and 1880; Pennsylvania German Pioneers, for Germans who arrived between 1727 and 1808 and signed oaths of allegiance; Index to Emigrants From Sweden to The Port of New York City (a microfilm index), for Swedes who arrived between 1851 and 1869; and many others.

In the last 25 years, many indexes of immigration records have been published. In 1981 P. William Filby and Mary K. Meyer, editors, published three volumes containing approximately 700,000 personal names, arranged alphabetically and gleaned from printed lists or compilations. The indexes include age (if given), destination, year of arrival, a source code, and a page number. They have since published many supplements, a great contribution to genealogists. The indexes are easy to use, especially since immigrants with multiple given name are indexed under each name, and known family members are separately indexed. In using these books, you must check both the original volumes and each of the supplements to see everything which Filby and Meyer have indexed to date. Remember also that the books include entries from printed records rather than from original passenger arrival records.

Passenger lists (manifests) and arrival lists are among the most important sources of information. Official lists are available from 1820 through 1945 for most ports in the United States which had customhouses. "Free cities" such as Baltimore may have kept separate passenger lists. There are, however, many gaps in arrival records. No lists were made of immigrants who entered through Canada or Mexico during the nineteenth century, and immigrants who arrived at the myriad of minor U.S. ports often were not accounted for. Pre-1820 arrivals are sometimes available in ships' logs or cargo manifests, which may be found in the local seaport museums or historical societies, but some masters did not list the passengers at all and included them simply as a particular number of pounds being shipped! Most of these passengers were dropped off in small harbors with no customhouses to avoid head taxes and possible enforced returns of illegal or sick passengers. Even after 1820, cargo vessels often listed passengers only on the ship's manifest.

By 1820, passenger ships had become common and immigration was regulated. Each ship was required to submit an official list of passengers to the collector of customs. A copy was also kept by the master and filed with the ship's papers. Original lists are extant for only seven U.S. ports; however, copies or abstracts of the original lists were sent quarterly to the Secretary of State, and many more of these documents have survived. The National Archives now has a microfilm copy of passenger lists of the ships in each U.S. port between 1820 and 1954 which were turned over by the Customs Service and the Immigration and Naturalization Service when the U.S government established the National Archives in 1935. It is thought, however, that from 10 to 40% of the lists were never sent and are, therefore, unavailable at the Archives. The missing records must be sought in local port customhouses or, in the case of some late acquisitions (especially for the West Coast ports), in the certain regions of the National Archives system.

The many lists sent to the National Archives are now available on microfilm, either in original form or as abstracts, at both the National Archives and the FHL and its branches (family history centers). Finding your ancestor in these records can, however, be a challenge. Some extremely valuable card indexes were made for the National Archives by the Work Projects Administration (WPA) during the Depression, but unfortunately, the project was never completed. Those available on microfilm are:

The first task in finding your immigrant ancestor in these records is to find out as much information as you can about him or her in America. By gathering marriage and death records, land deeds, county histories, naturalization papers, etc., you may be able to at least guess the nationality and the approximate year and place of the ancestor's arrival.

To search immigration records, choose the most likely index and follow the directions, generally available at the library, as to whether to use an alphabetical or a Soundex search system. Before beginning, you should also familiarize yourself with the format of the cards for the time period and port you are seeking, thus narrowing your search. Before 1897 little information was requested from the passengers other than their name, age, occupation, and nationality, so the indexes also contain little more than names and arrival dates. Cards for 1897 to 1902 contain practically all information found in the original records, often including a town of origin and next of kin in the United States. Except for the port of New York, cards for immigrants from 1903 to 1910 may be identifiable only by the immigrant's name and arrival year, as they do not include an age. Cards for the port of New York during this period contain more information. Cards for immigrants from 1910 to 1937 show name and age, but no arrival year. These cards can be further identified by comparing the volume number with a list of the years covered in particular volumes.

Once you have located your ancestor or possibilities in the indexes, search the actual ships' lists for the records from which the card was made. Especially in more recent years, you may find much information.