Väsen is a Swedish folk music band from Uppsala, founded in 1989, consisting of Olov Johansson (nyckelharpa) and Mikael Marin (viola). Previous members include André Ferrari (percussion) and Roger Tallroth (guitar), the latter of whom announced his departure from the band in 2020 to focus on new projects. As of 2019 they have released 19 albums, featured on others, and have toured every year also outside of Europe. Since 2002, however, performances outside Sweden have tended to not include André Ferrari, owing to his reluctance to tour internationally and the economic advantage of a trio. Since then, Väsen has released eight albums (Trio, Keyed Up, Live in Japan, Väsen Street, Mindset, Live på Gamla Bion, Brewed, & Rule of 3) in this “strings-only” format.
The band played on Nordman's debut album in 1994. On the Finnish group JPP's album String Tease, they were guest artists on two of the tracks.
They also regularly play with the American musicians Mike Marshall (mandolin) and Darol Anger (violin).