Abstract: An infrared seeker head for target tracking missiles has a main detector and an imaging optical system generating an image of a field of view on the main detector. The field of view contains a target such as an enemy aircraft. The missile is guided to the target in accordance with signals from the main detector. The target, if attacked by the missile, emits high-intensity laser radiation towards the missile as a counter-measure. This is to disturb the operation of the seeker head by dazzling or even destroying the main detector. The seeker head contains a device for defending against such disturbances. Various types of such defending devices are described. Incident light is deviated from the main detector. A second-quadrant-detector of reduced sensitivity guides the missile along the disturbing laser beam. Another embodiment uses attenuating optical elements in front of the main detector under the control of one or more second detectors.