The Butte, Anaconda and Pacific Railway is a short line railroad in the U.S. state of Montana which was founded in 1892. It was financed by the interests behind the Anaconda Copper Mining Company and operated primarily to carry copper ore from the mines at Butte, Montana to the smelters at Anaconda, Montana, although the company was chartered as a common carrier and also carried passengers and general freight.

The BA&P was an electrification pioneer, converting in 1913 and being the first primarily freight railroad to electrify. Electrification was at 2,400 Volts DC; the work was performed by General Electric and the railroad's own staff. The electrification was abandoned in 1967 as it had become cheaper to operate diesel-electric locomotives.

The railroad as a whole lost much of its business following the closure of the Anaconda smelters, and in 1985 was sold to a consortium of local investors and reconstituted as the Rarus Railway. On July 19, 2007, Patriot Rail Corporation, the parent company which acquired Rarus Railway in May 2007, announced that the railway's name was officially changed back to Butte, Anaconda and Pacific Railway.