The Janney Coupler is a semi-automatic railway coupler. The earliest commercially successful version of the Knuckle Coupler, it was patented by Eli H. Janney in 1873 (U.S. Patent 138,405).

In the United Kingdom, where it is fitted to some rolling stock, mostly for passenger trains, it is also known as a "Buckeye Coupler", possibly originating from the coupler's manufacture as early as 1890 by the Buckeye Steel Castings firm in Columbus, Ohio.