The Lanarkshire and Ayrshire Railway (L&AR) was an independent railway company built to provide the Caledonian Railway with a shorter route for mineral traffic from the coalfields of Lanarkshire to Ardrossan Harbour, in Scotland.
It opened in stages from 1888, being extended to Neilston and Newton, giving the Caledonian Railway a fully independent route by 1904. At the Ayrshire end the line duplicated the existing Glasgow and South Western Railway route at a time when bulk coal exports could be handled more economically in Clydebank, so that the primary purpose of the line was short-lived. The Caledonian Railway hoped to develop suburban traffic in south Glasgow where the new line passed through those districts, but street tramcars limited the success of this.
The duplicate routes to Ardrossan were wasteful and, as traffic declined, closures took place from 1930. The eastern section from Neilston and Newton to the Cathcart circle lines developed as outer suburban railways, and were electrified in the 1960s. Those branches, as they became, continue in intensive passenger use at the present day, but are the only remaining sections of the Lanarkshire and Ayrshire line remaining in operation.