In a device for guiding and braking a yarn, a yarn brake comprises braking elements that are pressed flexibly against each other and act on the yarn in a pinch zone. The yarn brake is arranged in the yarn running path between a yarn feeder and a yarn receiver. A pneumatic threader also is provided which includes at least one air and yarn guide element that is disposed in the yarn brake and surrounds the pinch zone without contact. The air and yarn guide element comprising a receiving end, a delivery end and a guide channel provided therebetween, which is open towards the braking elements and from which the yarn is introduced into the pinch zone. The yarn is conveyed into the guide channel by means of an air flow past the pinch zone to the yarn receiver and is introduced into the pinch zone under the action of a produced drawing force.