Ferdinand August Geiger (October 15, 1867 – July 31, 1939) was a United States federal judge.
Born in Cassville, Wisconsin, Geiger was in private practice in Milwaukee, Wisconsin from 1888 to 1912.
On February 19, 1912, Geiger was nominated by President William H. Taft to a seat on the United States District Court for the Eastern District of Wisconsin vacated by Joseph V. Quarles. Geiger was confirmed by the United States Senate on March 20, 1912, and received his commission the same day. Geiger served in that capacity until his retirement on May 22, 1939.