Marillion /məˈrɪljən/ are a British rock band, formed in Aylesbury, Buckinghamshire, England, in 1979. They emerged from the post-punk music scene in Britain and are credited with creating a bridge between the styles of punk rock and classic progressive rock, becoming the most commercially successful neo-progressive rock band of the 1980s. They have sold more than 15 million albums.

Marillion's recorded studio output since 1982 is composed of seventeen albums generally regarded in two distinct eras, delineated by the departure of original frontman Fish in late 1988, and the subsequent arrival of replacement Steve Hogarth in early 1989. The band achieved eight Top Ten UK albums between 1983 and 1994, including a number one album in 1985 with Misplaced Childhood, and during the period the band were fronted by Fish they scored eleven Top 40 hits on the UK Singles Chart. They are best known for the 1985 singles "Kayleigh" and "Lavender", which reached number two and number five respectively. The first album released with Hogarth, 1989's Seasons End, was another Top Ten hit, and albums continued to chart well until their departure from EMI following the release of their 1996 live album Made Again and the dissipation of the band's mainstream popularity in the late 1990s; save for a resurgence in the mid- to late-2000s, they have essentially been a cult act since then. Marillion have achieved a further twelve Top 40 hit singles in the UK with Hogarth, including 2004's "You're Gone", which charted at No. 7 and is the biggest hit of his tenure. The band continue to tour internationally, and were ranked 38th in Classic Rock's "50 Best Live Acts of All Time" in 2008.

Marillion are widely considered to have been one of the first mainstream acts to have fully recognised and tapped the potential for commercial musicians to interact with their fans via the internet, starting in around 1996, and are nowadays often characterised as a rock & roll 'Web Cottage Industry'. The history of the band's use of the Internet is described by Michael Lewis in the book Next: The Future Just Happened as an example of how the Internet is shifting power away from established elites, such as multinational record labels and record producers. The band are renowned for having an extremely dedicated following (often self-termed 'Freaks'), with some fans regularly travelling significant distances to attend single gigs, driven in large part by the close fan base involvement which the band cultivate via their website, podcasts, biennial conventions and regular fanclub publications. The release of their 2001 album Anoraknophobia, which was funded by their fans through advance orders instead of by the band signing to a record company, gained significant attention and was called "a unique funding campaign" by the BBC. Writing for The Guardian, Alexis Petridis described Marillion as "the undisputed pioneers" of fan-funded music.