Wim Mertens (Dutch pronunciation: [ʋɪˈmɛrtəns]; born 14 May 1953) is a Flemish Belgian composer, countertenor vocalist, pianist, guitarist, and musicologist.

Mertens' style has continually evolved during the course of his prolific career, starting from downright experimental and avant-garde, always gravitating around minimalism, usually, however, preserving a melodic foundation to the forays that he makes into the worlds that he is exploring.

His compositional quality has often overweighted the "labelling issue" and reached wider audiences although stemming from a far-from-mainstream musical context (see section In popular culture).

One can follow three separate threads of musical styles throughout his work: Mertens has released more than 60 albums to date, the majority of which were issued by Les Disques du Crépuscule from 1980 until 2004.

Mertens also produced a number of Crépuscule releases and consulted with the label on its choice of works by contemporary composers such as Michael Nyman, Gavin Bryars, and Glenn Branca.