Randolph Barnes Marcy (April 9, 1812 – November 22, 1887) was an officer in the United States Army, chiefly noted for his frontier guidebook, the Prairie Traveler (1859), based on his own extensive experience of pioneering in the west.

Here he prepared his acclaimed guidebook to the western trails, The Prairie Traveler: A Handbook for Overland Expeditions, with Maps, Illustrations, and Itineraries of the Principal Routes between the Mississippi and the Pacific.

Based on his own extensive experience of "more than thirty years of service in the United States Army, a large portion of the time on the frontiers"[3] and in the mountains, deserts, and prairies, the book provided authoritative advice about reconnaissance, fieldcraft, provisions and healthcare, that would save many lives on these perilous routes.

It covered key topics like food and water supply and hunting and tracking, and provided specialist advice about the selection of horses, avoiding quicksand, interpreting smoke signals and sign language, and numerous other issues.

Andrew J. Birtle, author of U.S. Army Counterinsurgency and Contingency Operations Doctrine 1860-1941, has described the Prairie Traveler as "perhaps the single most important work on the conduct of frontier expeditions published under the aegis of the War Department."