Väsen is a Swedishfolk music band originally consisting of Olov Johansson (nyckelharpa), Mikael Marin (viola) and Roger Tallroth (guitar). Later André Ferrari (percussion) also joined the group. As of 2015[update] they have released 16 albums, 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 six albums (Trio, Keyed Up, Live in Japan, Väsen Street, Mindset & Live på Gamla Bion) in this "strings-only" format.
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).