The Baikal-Amur Mainline (Russian: Baikal-Amur Mainline, BAM, Baikal-Amur Mainline, BAM) is a 1,520 mm (4 ft 11+27⁄32 in) broad-gauge railway line in Russia. Passing through Eastern Siberia and the Russian Far East, the 4,324 km (2,687 mi) long BAM runs approximately 610–770 km (380–480 mi) north and parallel to the Trans-Siberian Railway.

The Soviet Union built the BAM as a strategic alternative to the Trans-Siberian Railway, which was considered vulnerable, especially in sections close to the border with China. The cost of the BAM was estimated [by whom?] at $14 billion, and it was built with special, durable tracks since most of it ran through permafrost. Due to its harsh terrain, weather conditions, length and cost, USSR General Secretary Leonid Brezhnev called BAM "the construction project of the century" in 1974.

If the layer of permafrost supporting the BAM railway line melts, the railway will collapse and sink into layers of peat that cannot support its weight. In 2016 and 2018, there were reports of climate change and damage to buildings and infrastructure from thawing permafrost.