The Nilgiri Mountain Railway (NMR) is a 1,000 mm metre gauge railway in Nilgiris district, Tamil Nadu, India, built by the British in 1908. The railway is operated by the Southern Railway and is the only rack railway in India.

The Nilgiris district is one of the 38 districts in the southern Indian state of Tamil Nadu. Nilgiri is the name given to a range of mountains spread across the borders among the states of Tamil Nadu, Karnataka and Kerala. The Nilgiri Hills are part of a larger mountain chain known as the Western Ghats. Their highest point is the mountain of Doddabetta, height 2,637 m. The district is contained mainly within the Nilgiri Mountains range. The administrative headquarters is located at Ooty. The district is bounded by Coimbatore to the south, Erode to the east, and Chamarajnagar district of Karnataka and Wayanad district of Kerala to the north. As it is located at the junction of three states, namely, Tamil Nadu, Kerala, and Karnataka, significant Malayali and Kannadiga populations reside in the district. Nilgiris district is known for natural mines of Gold, which is also seen in the other parts of Nilgiri Biosphere Reserve extended in the neighbouring states of Karnataka and Kerala too.