The Highland Railway was one of the smaller British railways before the Railways Act 1921, operating north of Perth railway station in Scotland and serving the farthest north of Britain. Based in Inverness, the company was formed by merger in 1865, absorbing over of line. It continued to expand, reaching Wick and Thurso in the north and Kyle of Lochalsh in the west, eventually serving the counties of Caithness, Sutherland, Ross & Cromarty, Inverness, Perth, Nairn, Moray and Banff. Southward it connected with the Caledonian Railway at Stanley Junction, north of Perth, and eastward with the Great North of Scotland Railway at Boat of Garten, Elgin, Keith and Portessie.
In 1923, the company passed on approximately of line as it became part of the London, Midland and Scottish Railway. Although its shorter branches have closed, former Highland Railway lines remain open from Inverness to Wick and Thurso, Kyle of Lochalsh, Keith (as part of the Aberdeen to Inverness Line), as well as the direct main line south to Perth.
The Highland Railway main line between Inverness and Perth, which opened in 1863, left the Caledonian Railway at Stanley and then ran north over the Grampian Mountains. After 1898 the line followed a more direct route via , leaving the earlier line via at a junction at .
Between 1865 and 1965 the Highland operated one branch from to .
The Aberfeldy branch left the main line at Ballinluig. The line opened on 3 July 1865 and was closed to passengers on 3 May 1965.
An independent company built and opened the railway, and the line was taken over by the Inverness & Aberdeen Junction Railway 1862. The line was closed by the Highland in 1869.
The Far North Line between Inverness and Wick and Thurso opened in stages between 1862 and 1874. As well as the Kyle of Lochalsh Line that branches at Dingwell, the Black Isle Branch left at Muir of Ord for Fortrose, the Dornoch Light Railway left at The Mound for Dornoch and the Wick & Lybster Light Railway ran from Wick to Lybster.
The Kyle of Lochalsh Line leaves the Far North Line at Dingwall. Between 1885 and 1946 a branch left the line at Fodderty Junction, from Perth. The line was diverted in 1954, as part of a hydro electric project that raised the level of Loch Luichart, the distances are measured from Perth via this new line.
The Invergarry & Fort Augustus Railway was an isolated branch from that was worked by the Highland from when it opened in 1903 until 1 May 1907, when the North British Railway took over.