Louis Sclavis's first outing in a trio format is so successful that we are left wondering why he did not try this formula earlier. It appears to be such an appropriate setting to fully appreciate his impressive improvising skills. Although the opening track features Louis Sclavis on soprano saxophone, this session is primarily a stage for his clarinet playing - mainly, bass clarinet. "Qumrân" is a wonderful unaccompanied bass clarinet solo built on a thread of loops. Seconded by two faithful collaborators, bassist Bruno Chevillon and drummer François Merville, Sclavis surely gets adequate support. Both musicians provide an intricate and supple foundation, never relying on the same pattern. They are also very attentive musicians who can react at once to the leader's moves, and contribute some ideas of their own. Their complicity also allows Sclavis to explore various territories and moods. At times, the writing is peppered with touches of romanticism and dreaminess, and sometimes hints at another great European clarinetist, John Surman. As a consequence, the music definitely belongs to a European aesthetic - only the title-track betrays Sclavis' continued interest for Northern African music. It can also be qualified as cerebral, but it is never dry due to its occasional playfulness and unexpected bounciness. Finally, frequent shifts and time signature changes keep the listener on his/her toes. Ceux Qui Veillent La Nuit is the perfect place to sample Sclavis' original work and various approaches to his instrument.