This finding aid describes the Dr. James Carroll, Yellow Fever Commission Letters; the collection contains original letters to Janetta “Jennie” Carroll, Dr. Carroll’s wife as well as letters from Dr. Walter Reed, head of the United States Army Yellow Fever Commission in Cuba in 1900 and 1901. The research and experimentation completed by the Commission found that Yellow Fever was carried by Mosquitos and transmitted through their bites. The letters in this collection shed light on the research and experimentation process as well as the living conditions in Cuba during the Commission’s work. The letters provide a personal insight into the men who discovered the cause of Yellow Fever.