Three Years in Field Hospitals of the Army of the Potomac is a memoir written by American nurse and reformer, Mary Phinney von Olnhausen (1828-1902). The book was published in 1867 and chronicles Mary's experiences as a nurse during the American Civil War. Mary Phinney von Olnhausen was born in Massachusetts and was from a wealthy family. During the war, she volunteered as a nurse for the Union Army, working in field hospitals throughout the Eastern Theater of the war. She served in various hospitals including the U.S. Army General Hospital in Frederick, Maryland, and the Armory Square Hospital in Washington D.C. She was known for her dedication to the care of wounded soldiers and her efforts to improve the conditions in the hospitals where she worked. In Three Years in Field Hospitals of the Army of the Potomac, Mary provides a firsthand account of the challenges and difficulties faced by nurses during the war. She describes the primitive medical facilities, the shortage of medical supplies, and the struggles of tending to injured soldiers under fire. Her book also includes details about the experiences of wounded soldiers, including their medical treatments and the emotional toll of being away from home and family during the war. After the war, Mary continued her nursing career and worked to improve healthcare in the United States. She helped establish the Women's Medical College of Pennsylvania and served as the superintendent of the New England Hospital for Women and Children. Mary Phinney von Olnhausen's Three Years in Field Hospitals of the Army of the Potomac is a significant contribution to the history of nursing during the Civil War and remains an important primary source for researchers and historians interested in this period.