The Spontaneous Music Ensemble (SME) was a loose collection of free improvising musicians, convened in 1965 by the now late South London-based jazz drummer/trumpeter John Stevens and alto and soprano saxophonist Trevor Watts. SME performances and recordings could range from Stevens–Watts duos to gatherings of more than a dozen players.

As critic Brian Olewnick writes, the SME emphasised an "extremely open, leaderless aspect where a premium was placed on careful and considered listening on the part of the musicians. Saxophonist Evan Parker observed that Stevens had two basic rules: (1) If you can't hear another musician, you're playing too loud, and (2) if the music you're producing doesn't regularly relate to what you're hearing others create, why be in the group? This led to the development of what would jocularly become known as 'insect improv' – music that tended to be very quiet, very intense, arrhythmic, and by and large atonal."