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About the Official Records [click here]
No serious study of the American Civil War is complete without consulting the Official Records. Affectionately known as the "OR", the 128 volumes of the Official Records provide the most comprehensive, authoritative, and voluminous reference on Civil War operations.
Index of the Official Records by Series or Volume [click here]
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Companion Atlas to the Official Records [click here]
From the about link:
Officially titled, The War of the Rebellion: A Compilation of the Official Records of the Union and Confederate Armies, the Official Records are compiled in 127 volumes, plus a General Index and accompanying Atlas. Editor Robert N. Scott divided the OR into four major topical areas:
Series I contains 53 volumes (Books 1-111) and focuses on military operations. These include the battle reports for both Union and Confederate armies, arranged chronologically by campaign and theater of operations. Union reports are followed by Confederate accounts. The intent is to provide a complete history of the event in the same volume.
Series II contains 8 volumes and 8 books, and includes Union and Confederate correspondence, orders, reports, and returns relating to Prisoners of War, as well as political prisoners.
Series III contains 5 volumes and 5 books, and includes "miscellaneous" Union correspondence, orders, and reports pertaining to the organization and logistics of the Union war effort. Series III also includes calls for troops, correspondence between National and State authorities, and correspondence between Union and Confederate authorities.
Series IV contains 3 volumes and 3 books, and includes "miscellaneous" correspondence, orders, and reports of the Confederacy. Also found in Series IV are the General and Special Orders of the Confederate States Army, as well as correspondence relating to conscription and blockage running.
A word of caution must be made here about the value and limitations of the Official Records. As primary source material, the Official Records are, without question, the most complete and impartial documentation on the American Civil War. They provide a foundation for serious research into virtually any aspect of the war. On the other hand, no study of the American Civil War should rely exclusively on the Official Records. The accounts contained in the OR were not edited for accuracy, and due to space considerations, only excerpts of reports were often included. Researchers should thus verify the information found in these reports with other source material to gain as complete a picture of events as possible.