Iain Matthews (born Ian Matthews MacDonald, 16 June 1946) is an English musician and singer-songwriter. He was an original member of the British folk rock band Fairport Convention from 1967 to 1969 before leaving to form his own band, Matthews Southern Comfort, which had a UK number one in 1970 with their cover of Joni Mitchell's "Woodstock". In 1979, his recording of Terence Boylan's "Shake It" reached No. 13 on the US charts.

Born in Barton-upon-Humber, Lincolnshire, Matthews was known in the 1960s as Ian MacDonald. He changed his name to Ian Matthews (his mother's maiden name) in 1968 to avoid confusion with Ian McDonald of King Crimson. In 1989 he changed the spelling of his first name to Iain, and has been known as Iain Matthews ever since.

Influenced by both rock and roll and folk music, Matthews has performed solo and as a member of various bands. He was a member of Fairport Convention during the band's early period when they were heavily influenced by American folk rock and sang on their first three albums before leaving in 1969. He initially embarked upon a solo career before forming the bands Matthews Southern Comfort and Plainsong. Later in his career he was also a member of the bands Hi-Fi, No Grey Faith, and More Than a Song. In the 2000s he twice revived Plainsong and Matthews Southern Comfort (MSC) and continues to tour regularly with the current version of MSC. A new MSC album, The New Mine, was released in March 2020, and a vinyl-only album Fake Tan, recorded with Norwegian band the Salmon Smokers, was released in September 2020.

In a career spanning over fifty years, Matthews has featured on over 100 albums. In 2018 he published an autobiography co-written with author and broadcaster Ian Clayton, Thro' My Eyes: A Memoir, about his life in the music industry.