A servo valve comprising: first and second nozzles (12a, 12b); and first and second piezoelectric actuators (14a, 14b) arranged to control fluid flow through the first and second nozzles (12a, 12b) respectively, wherein: a first fluid flow path is defined between the first nozzle and the first piezoelectric actuator; a second fluid flow path is defined between the second nozzle and the second piezoelectric actuator; and the first and second piezoelectric actuators (14a, 14b) are arranged such that applying a voltage to the first and second piezoelectric actuators (14a, 14b) causes a change in dimension thereof, which acts to open or restrict said first and second fluid flow paths respectively; the servo valve further comprising: a servo valve housing including a pair of nozzle cavities (18a, 18b), each housing a respective nozzle (12a, 12b) and piezoelectric actuator (14a, 14b), wherein the piezoelectric actuators (14a, 14b) are retained in the nozzle cavities (18a, 18b) by contact between a first axial end of each piezoelectric actuator (14a, 14b) opposite a second axial end facing the nozzle (12a, 12b) and a wall defined by the respective nozzle cavity (18a, 18b); characterised in that: the wall is a common wall shared by the first and second nozzle cavities (18a, 18b) and separating the first and second nozzle cavities (18a, 18b). first and second nozzles (12a, 12b); and first and second piezoelectric actuators (14a, 14b) arranged to control fluid flow through the first and second nozzles (12a, 12b) respectively, wherein: a first fluid flow path is defined between the first nozzle and the first piezoelectric actuator; a second fluid flow path is defined between the second nozzle and the second piezoelectric actuator; and the first and second piezoelectric actuators (14a, 14b) are arranged such that applying a voltage to the first and second piezoelectric actuators (14a, 14b) causes a change in dimension thereof, which acts to open or restrict said first and second fluid flow paths respectively; a first fluid flow path is defined between the first nozzle and the first piezoelectric actuator; a second fluid flow path is defined between the second nozzle and the second piezoelectric actuator; and the first and second piezoelectric actuators (14a, 14b) are arranged such that applying a voltage to the first and second piezoelectric actuators (14a, 14b) causes a change in dimension thereof, which acts to open or restrict said first and second fluid flow paths respectively; the servo valve further comprising: a servo valve housing including a pair of nozzle cavities (18a, 18b), each housing a respective nozzle (12a, 12b) and piezoelectric actuator (14a, 14b), wherein the piezoelectric actuators (14a, 14b) are retained in the nozzle cavities (18a, 18b) by contact between a first axial end of each piezoelectric actuator (14a, 14b) opposite a second axial end facing the nozzle (12a, 12b) and a wall defined by the respective nozzle cavity (18a, 18b); a servo valve housing including a pair of nozzle cavities (18a, 18b), each housing a respective nozzle (12a, 12b) and piezoelectric actuator (14a, 14b), wherein the piezoelectric actuators (14a, 14b) are retained in the nozzle cavities (18a, 18b) by contact between a first axial end of each piezoelectric actuator (14a, 14b) opposite a second axial end facing the nozzle (12a, 12b) and a wall defined by the respective nozzle cavity (18a, 18b); characterised in that: the wall is a common wall shared by the first and second nozzle cavities (18a, 18b) and separating the first and second nozzle cavities (18a, 18b).