Soldier and explorer William H. Emory traveled the length and breadth of the United States and participated in some of the most significant events of the nineteenth century. This first complete biography of Emory offers new insight on this often overlooked figure and provides an important look at an expanding America. Emory was a West Point graduate who became a civil engineer with the newly formed Corps of Topographical Engineers. He was selected to accompany Stephen Watts Kearny and the Army of the West in their trek to California in 1846, and his map from that expedition helped guide Forty-Niners bound for the goldfields. He then worked for nine years on the new border between the United States and Mexico. When the Civil War broke out, he commanded a regiment defending Washington, D.C., and later saw action at Manassas, in the Red River campaign, and in the Shenandoah Valley, where he served under Phil Sheridan. This biography draws on Emory's personal papers to reveal other significant episodes of his life. While commanding a cavalry unit in the Indian Territory, he was the only officer to bring an entire command out of insurrectionary territory; in hostile action of a different kind, he was a major witness in the impeachment trial of Andrew Johnson and offered testimony that helped save the president. William H. Emory: Soldier-Scientist is an important resource for scholars of western expansion and the Civil War. More than that, it is a rousing story of an unsung but distinguished hero of his age.