S-mount is a variation of mount control where one sits on top of an opponent whose back is to the ground, but with one knee up on one side and one knee down on the other, making what resembles an S shape with the legs. This variation of a basic mount control is useful in preparation for moving the knee that is off the ground into other positions, such as to pivot into an armbar submission, to set up transitions to other positions such as side control, or for other uses such as to use the knees for various pressures on the opponent.

While S-mount is not quite a fundamental position of Brazilian Jiu-Jitsu, it is an essential position in one's toolbox of positions.