One of the core tenets of Mormon faith is that the dead can be baptized into the faith after their passing. Baptism of the dead evolved from the beliefs that baptism is necessary for salvation and that the family unit can continue to exist together beyond mortal life if all members are baptized.

Mormons trace their family trees to find the names of ancestors who died without learning about the restored Mormon Gospel so that these relatives from past generations can be baptized by proxy in the temple. For Latter-day Saints, genealogy is a way to save more souls and strengthen the eternal family unit.

Original records -- about 2.4 million rolls of microfilm containing 2 billion names that have been traced -- are locked away behind 14-ton doors in the Granite Mountain Records Vault, a climate-controlled repository designed to survive a nuclear impact that is built into the Wasatch mountain range, about 20 miles southeast of Salt Lake City.

The practice has not been without controversy, however. In the mid-1990s, there was a backlash when it was uncovered that the names of about 380,000 Jewish Holocaust victims had been submitted for posthumous baptism by what church historian Marlin Jensen calls "well-intentioned, sometimes slightly overzealous members." In 1995, the church agreed to remove the names of all Holocaust victims and survivors from its archives and to stop baptizing Jews unless they were direct ancestors of a Mormon or unless they had the permission of all the person's living relatives. However, Jewish names have periodically been discovered since the 1995 agreement, including that of Holocaust survivor and Jewish human rights activist Simon Wiesenthal, which was found and removed in 2006. Catholics and members of other faiths have also been upset at the practice.

Despite the controversies, the Mormon archives are a boon to professional and amateur genealogists. Copies of the original microfilms are freely available at the Family History Library in Salt Lake City, which is the main repository, and they can be ordered at smaller regional Family History Centers. The records include vital records (birth, death and marriage certificates), wills and probate records, land records, town or county records, church records and more.

Much of the information is online at FamilySearch.org, which has several types of databases:

The International Genealogical Index (IGI) consists of two kinds of information: primary records typically gathered by Mormon missionaries and transcribed and indexed by Mormon and non-Mormon volunteers; and copies of ordinances provided by members of the church.

The Ancestral File has more than 35 million names organized into families and pedigrees. The information is not sourced, though typically you can find the name and address of the person who submitted the information so you can contact the submitter for further information. The Ancestral File stopped taking submissions in 2003; new submissions are added to the Pedigree Resource File. Anyone can submit information to the Pedigree Resource File; like the Ancestral File, the submitter's name is indicated.

The church created an index for every person counted in the 1880 U.S. census, the 1881 Canadian census and the 1881 British census. These records are freely available online, and images can be accessed at the Family History Library or a Family History Center.

Other records online through FamilySearch.org include the Social Security Death Index, which has the names of deceased individuals who had a Social Security card and whose death was reported to the Social Security Administration after 1962 (when the database began); and the Vital Records Index, which has birth, death, christening and marriage records for select localities in Mexico and Scandinavia.

In 2001, the LDS Church collaborated with the Ellis Island Foundation to build the American Family Immigration History Center and the Ellis Island Web site, which has the names of 22 million passengers and crew members who arrived in New York through Ellis Island between 1882 and 1924.

And in 2002, the LDS Church began an ambitious plan to scan and put online all of the billions of records in the Granite Mountain Vault, with volunteers creating indices to the records. Because of technological advances, a project once estimated to take 120 years may be finished in the next 10 years.