The Glasgow and South Western Railway (G&SWR) was a railway company in Scotland. It served a triangular area of south-west Scotland between Glasgow, Stranraer and Carlisle. It was formed on 28 October 1850 by the merger of two earlier railways, the Glasgow, Paisley, Kilmarnock and Ayr Railway and the Glasgow, Dumfries and Carlisle Railway. Already established in Ayrshire, it consolidated its position there and extended southwards, eventually reaching Stranraer. Its main business was mineral traffic, especially coal, and passengers, but its more southerly territory was very thinly populated and local traffic, passenger and goods, was limited, while operationally parts of its network were difficult.

The Glasgow, Paisley, Kilmarnock and Ayr Railway (GPK&AR) was a railway in Scotland that provided train services between Glasgow, Kilmarnock and Ayr. It opened its first line, between Glasgow and Ayr, in stages from 1839 to 1840. The section between Glasgow and Paisley was made jointly with the Glasgow, Paisley and Greenock Railway. Later it built a line from Dalry via Kilmarnock to Cumnock, linking there with the Glasgow, Dumfries and Carlisle Railway, and together forming a through route from Glasgow to Carlisle. The two companies merged to form the Glasgow and South Western Railway.