An adjustable and foldable shoulder rest for a violin or viola, the shoulder rest comprising: a shoulder-engaging body having a first end and a second end, the body also having a shoulder-engaging side and an instrument-facing side; a first foldable fork-shaped clamping member disposed at the first end for clamping the violin or viola, wherein the clamping member is foldable from an unfolded position to a folded position; a second foldable fork-shaped clamping member disposed at the second end for clamping the violin or viola wherein the clamping member is foldable from an unfolded position to a folded position; a first slidable end member for receiving a threaded stem that supports the first clamping member, the first slidable end member being slidable between a retracted position and an extended position, the first slidable end member also having first and second arcuate channels (150, 152) through which the stem rotates as the first clamping member is pivoted between the unfolded and folded positions, wherein the first slidable end member is slidable within a first slot in the instrument-facing side of the body to extend or retract the first clamping member; a second slidable end member for supporting the second clamping member, the second slidable end member being slidable between a retracted position and an extended position, the second slidable end member also having first and second arcuate channels (150, 152) through which the stem rotates as the second clamping member is pivoted between the unfolded and folded positions, wherein the second slidable end member is slidable within a second slot in the instrument-facing side of the body to extend or retract the second clamping member; wherein the first slidable end member comprises a first protrusion shaped to engage one of a first plurality of apertures disposed in the first slot; wherein the second slidable end member comprises a second protrusion shaped to engage one of a second plurality of apertures disposed in the second slot; and wherein each of the first and second slidable end members (100, 110) comprises a pull-tab adjustable slider (102, 112) that flexes when pulled away from the slot to disengage the protrusion from the aperture, the pull-tab adjustable slider (102, 112) being elastically biased to return to an unflexed posture against the slot. a shoulder-engaging body having a first end and a second end, the body also having a shoulder-engaging side and an instrument-facing side; a first foldable fork-shaped clamping member disposed at the first end for clamping the violin or viola, wherein the clamping member is foldable from an unfolded position to a folded position; a second foldable fork-shaped clamping member disposed at the second end for clamping the violin or viola wherein the clamping member is foldable from an unfolded position to a folded position; a first slidable end member for receiving a threaded stem that supports the first clamping member, the first slidable end member being slidable between a retracted position and an extended position, the first slidable end member also having first and second arcuate channels (150, 152) through which the stem rotates as the first clamping member is pivoted between the unfolded and folded positions, wherein the first slidable end member is slidable within a first slot in the instrument-facing side of the body to extend or retract the first clamping member; a second slidable end member for supporting the second clamping member, the second slidable end member being slidable between a retracted position and an extended position, the second slidable end member also having first and second arcuate channels (150, 152) through which the stem rotates as the second clamping member is pivoted between the unfolded and folded positions, wherein the second slidable end member is slidable within a second slot in the instrument-facing side of the body to extend or retract the second clamping member; wherein the first slidable end member comprises a first protrusion shaped to engage one of a first plurality of apertures disposed in the first slot; wherein the second slidable end member comprises a second protrusion shaped to engage one of a second plurality of apertures disposed in the second slot; and wherein each of the first and second slidable end members (100, 110) comprises a pull-tab adjustable slider (102, 112) that flexes when pulled away from the slot to disengage the protrusion from the aperture, the pull-tab adjustable slider (102, 112) being elastically biased to return to an unflexed posture against the slot.