Walter Reed (September 13, 1851 - November 23, 1902) was an American Army surgeon who led the team which proved the theory first set forth in 1881 by the Cuban doctor and scientist Dr. Carlos Finlay that yellow fever is transmitted by mosquitoes rather than direct contact.

Soon after graduation from the University of Virginia, Reed became a medical officer with the US Army in a time of great advances in medicine due to widespread acceptance of Louis Pasteur's germ theory of disease as well as the methods of studying bacteria developed by Robert Koch. Reed worked closely with George Miller Sternberg, the Army Surgeon General, who was one of the founders of bacteriology.

Yellow fever became a problem for the Army during the Spanish American War, when the disease felled thousands of soldiers in Cuba. In May 1900, Reed, a major, was appointed president of a board "to study infectious diseases in Cuba paying particular attention to yellow fever." This board eventually proved both the transmission by mosquitoes and disproved the common belief that yellow fever could be transmitted by clothing and bedding soiled by the body fluids and excrement of yellow fever sufferers - articles known as fomites. His work with the disease was largely responsible for stemming the mortality rates from yellow fever during the building of the Panama Canal in the early 1900's, something that had confounded the French attempt to build in that region only 30 years earlier.

After this work, Reed resumed his position as professor of bacteriology in the Army Medical School, and as professor of pathology and bacteriology at the George Washington University Medical School. His health had been in decline following an appendectomy, and he died of peritonitis. He was buried in Arlington National Cemetery.

In 1929, the Walter Reed Medal was awarded posthumously to Walter Reed for his work in discovering the cause of yellow fever. Walter Reed Army Medical Center in Washington, D.C. is also named after him.