Robert Chambers Reamer (1873–1938) was an American architect, most noted for the Old Faithful Inn in Yellowstone National Park. A number of his works are listed on the National Register of Historic Places for their architecture.

Reamer was born in and spent his early life in Oberlin, Ohio. He left home at the age of thirteen and went to work in an architect's office in Detroit as a draftsman.

By the age of twenty-one, Reamer had moved to San Diego and had opened the architectural office of Zimmer & Reamer in partnership with Samuel B. Zimmer. The firm produced a wide variety of projects, but the only surviving example of Zimmer & Reamer's work is the George H. Hill Block in the Gaslamp District. The partnership dissolved in 1898, but Reamer continued to work on his own, including work at the Hotel del Coronado. During this period he became acquainted with the president of the Yellowstone Park Company, Harry W. Child.