BAI Bretagne Angleterre Irlande S.A. trading as Brittany Ferries is a French shipping company based in Roscoff, France. Founded in 1973 by Alexis Gourvennec, it operates passenger and freight services between the Channel Islands, France, Ireland, Spain and the United Kingdom.

BAI (Bretagne Angleterre Irlande) S.A. was founded by Alexis Gourvennec. Working with fellow Breton farmers, Gourvennec lobbied for improvements to Brittany's infrastructure, including better roads, telephone network, education and port access. By 1972, he had successfully secured funding and work to develop a deep-water port at Roscoff. Gourvennec had no desire to run a ferry service, but existing operators showed little appetite for the opportunity.

The company itself began sailings on 2 January 1973 between Roscoff in Brittany and Plymouth in the South West of England, using the freight ferry Kerisnel, a former Israeli tank carrier. The company's primary aim at that time was to exploit opportunities presented by the UK's entry into the European Common Market, forerunner to the European Union, in order to export directly to markets in the United Kingdom.

In 1974, Kerisnel was replaced by Penn-Ar-Bed, which carried both passengers and vehicles, and the BAI company adopted the name Brittany Ferries.

It was revealed in the press in May 1985 that Truckline Ferries was in discussions about a takeover of the company (which was by now fully French-owned), with bids coming from Sealink British Ferries, owned by Sea Containers, and Brittany Ferries. Both initial bids were refused, but in July 1985, Brittany announced they had purchased the Truckline companies Worms and CGM for an undisclosed amount. The Truckline name was to be retained on the Poole-Cherbourg service along with staff and the existing fleet and an immediate £3.5 million cash injection was made to develop the service further. This resulted in two major moves by the company; the first to 'jumboize' the freight ships Coutances and Purbeck, which took place in the first half of 1986, the second was to introduce a new passenger service under the Truckline brand during the summer season from June 1986. As a result of the takeover, Brittany Ferries became the largest freight ferry operator on the Western Channel.

In 1990 Brittany Ferries joined forces with Emeraude Ferries and British Channel Island Ferries to launch a 'French Connection' service which would allow a Poole-Jersey, Jersey-St. Malo, St Malo-Portsmouth round trip to be booked as a single journey across the three operators.

Operations under the Truckline name ceased in 1999, when Brittany Ferries rebranded the service under their own name.

In 2001, Brittany Ferries launched a joint service with Condor Ferries for fast ferry services between Poole and Cherbourg during the summer. The Condor Vitesse was used with dual-branding of both companies. Between 2022 and 2023, Condor operated summer weekend services between, Portsmouth, Cherbourg and Poole using the Condor Liberation.