Ardrossan (/ɑːrˈdrɒsən/; from Scottish Gaelic Àird Rosain 'headland of the small promontory') is a town on the North Ayrshire coast in southwestern Scotland. The town has a population of 10,670 and forms part of a conurbation with Saltcoats and Stevenston known as the 'Three Towns'. Ardrossan is located on the east shore of the Firth of Clyde, and is the main terminal of Caledonian MacBrayne ferry services operating from mainland Scotland to the Isle of Arran.

The town is home to the Ardrossan Wind Farm, and is home to a number of businesses and organisations including Cunningham Housing Association. The town is served by two secondary schools – Ardrossan Academy and St Matthews Academy. A new 2–18 curriculum campus is currently under construction, and will include Ardrossan Academy and Winton Primary School & Early Years on the former Shell oil refinery site.

Ardrossan's roots can be traced to the construction of its castle 'Cannon Hill', thought to be in around 1140, by Simon de Morville. The castle and estate passed to the Barclay family (also known as Craig) and through successive heirs until the 14th century when it passed to the Eglinton family on the death of Godfrey Barclay de Ardrossan, who died without an heir. Sir Fergus Barclay, Baron of Ardrossan, was said to be in league with the Devil and in one of his dealings, set the task for the Devil to make ropes from sand; on failing to do so, the Devil kicked the castle with his hoof in frustration and left a petrosomatoglyph hoofprint. The castle stood until 1648, when Oliver Cromwell's troops had it destroyed, taking much of the stonework to Ayr to build the citadel at Montgomerieston. The ruins of Cromwell's Fort still stand, but are overgrown and in a dangerous condition.

In 1759, The 10th Earl of Eglinton formed a herd of the ancient breed of White or Chillingham cattle at Ardrossan, probably using stock from the Cadzow herd. The numbers dropped and in 1820 the remaining animals were dispersed. All the animals in the herd were hornless.

Ardrossan developed during the 18th and 19th centuries thanks to its position on the coast. Exports of coal and pig iron to Europe and North America were the main trade from the town's port, which became a centre for shipbuilding. Fishing vessels and small cargo boats were the mainstay of the shipyard until the 1950s, when the yard ceased to exist as a result of foreign competition. A smaller yard, McCrindle's, operated until the 1980s before it ceased trading.

Passenger services from Ardrossan Harbour to Brodick on the Isle of Arran started in 1834, and services to Belfast, in Ulster in the north of Ireland, and to the Isle of Man followed in 1863 and 1892 respectively. Clyde sailings were operated initially by the Glasgow and South Western Railway Company from Winton Pier and the Caledonian Railway from Montgomerie Pier. The Earl of Eglinton's ambitious plan for a canal link to Glasgow was never realised.

Between 1841 and 1848, Ardrossan was a part of the "West Coast Main Line" equivalent of its time. The fastest route from London to Glasgow was by train to Fleetwood, and then by packet boat to Ardrossan. After 1848 the entire journey could be made by rail, avoiding Ardrossan. The link to the Isle of Man no longer operates, having first been moved to Stranraer until all Scottish services terminated. Shell-Mex operated an [oil refinery] on behalf of the Air Ministry, from a Second World War aviation-fuel canning factory, and the harbour was expanded for the company's tanker ships to berth.

The harbour has been redeveloped as a marina, and the passenger and vehicle ferry to Brodick is operated by Caledonian MacBrayne.