Until its soldiers mustered out of service in mid-1864, the Pennsylvania Reserve Division was one of only a few one-state divisions in the Union army. Known as the Pennsylvania Reserves, or simply the Reserves, the division saw action in most of the major battles of the Civil War, including Mechanicsville, New Market Crossroads, Second Bull Run, Fredericksburg, Gettysburg, the Wilderness, and Spotsylvania Court House. This history chronicles the division's service from its organization in May 1861 through June 1864, when most of its soldiers reached the end of their service commitment. The book includes short biographical sketches, most with photographs, of the Reserves leadership. Throughout, excerpts from letters, journals, diaries, and books from more than 150 members of the Reserves provide a personal perspective on the action and reveal the human side of battle.