An adjusting valve adjusting valve for adjusting the delivery volume of a displacement pump includes a valve casing, a valve piston which is mounted such that the valve piston can be moved within the valve casing, a valve spring which counteracts a force exerted by the valve-actuating pressure on the valve piston, and an adjusting device serving to adjust the valve piston in the direction of or counter to the force exerted by the valve-actuating pressure. A displacement pump exhibiting an adjustable delivery volume, includes a pump casing, a delivery chamber formed in the pump casing and a delivery member and the adjusting valve for adjusting the delivery volume, arranged in a flow of the fluid delivered by the delivery member.