The first step to determining whether you have ancestors who served in the military during the Civil War is to trace your genealogy back to the 1860s. If you have not already completed this step, the Library's "Genealogical Records at The Library of Virginia" pamphlet provides an excellent overview of the records in our collections that could be useful to your research.
After you have compiled a list of names of individuals who could have served in the military, you need to determine the unit(s) in which those individuals served. Several indexes can provide that information: Janet B. Hewett's Roster of Confederate Soldiers, 1861–1865 or Roster of Union Soldiers, 1861–1865 or the online Civil War Soldiers and Sailors System. These sources provide an index to the National Archives and Records Administration's compiled military service records (CMSRs), which were created primarily by abstracting information from Union and Confederate records that were housed at the National Archives during the early twentieth century. Most soldiers have a CMSR. Because misspellings abound in the records that were used to create the CMSRs, you will need to check all possible misspellings of your ancestors' surnames and remember that first and middle names may be reduced to initials. You may find listings for several individuals who could be your ancestor. Although your ancestor could have served in more than one unit, it is likely that you will need to narrow your list of units in which he may have served.
Next, you will need to limit your list by finding information on each soldier. If your ancestor was a Confederate who served in a Virginia unit, the fastest way to narrow your list may be to consult the Virginia Regimental Histories Series, which provides a history of a unit and information on the individuals who served with it. Look for several clues—it is likely that the unit was formed in or near the area in which your ancestor or his friends and family resided, and if you know that your ancestor survived the war and one of the potential matches did not, then you can eliminate him from your list. Lee A. Wallace Jr.'s compilation A Guide to Virginia Military Organizations 1861–1865, Rev. 2d ed. (Lynchburg, Va.: H. E. Howard, 1986), Stewart Sifakis's Compendium of the Confederate Armies: Virginia, and the other Confederate States in 10 vols. (New York: Facts on File, 1992–1995), and Joseph H. Crute's Units of the Confederate States Armies (Midlothian, Va.: Derwent Books, 1987) provide brief unit histories that could be helpful to your research since they often note the counties in which individual units or companies were formed. If your ancestor served in the Union military, Frederick H. Dyer's compilation A Compendium of the War of the Rebellion, 2 vols.([New York]: National Historical Society; Dayton, Ohio: Press of Morningside Bookshop, 1979) provides unit histories. C. E. Dornbusch's Military Bibliography of the Civil War (1961–1962; reprint, New York: New York Public Library, 1975–2003) provides a list of other unit histories that could provide information on your ancestor. If these sources do not help, you will need to obtain a copy of each potential ancestor's CMSR to gain information on those individuals.
Once you have identified the unit in which your ancestor served, you can search for information on his military service. If you have not already done so, order a copy of your ancestor's CMSR from the National Archives (or print a copy from the Library of Virginia's microfilm copy of the record while you at the Library) because this record is the most likely source of a significant amount of information on his military service. Next, begin a search for even more information. Although his name may be included in indexes and catalogs, you are more likely to find information on him by researching his unit because records are more often cataloged by unit and not by the individual names that they contain. Even if a record for your ancestor's unit does not mention his name specifically, you can learn what the unit—and mostly likely your ancestor—was doing at a particular time and place. Published sources may be found through the Library's Books and Journals Catalog, and unpublished sources may be found through the Library's Archives and Manuscripts Catalog and Military Service Web page.