This chapter provides an overview of visual fatigue and discomfort, both in terms of the mechanisms involved in the human visual system (HVS) and in terms of 3D content and processing technologies. It begins by defining the notions of fatigue and discomfort. A section provides an overview of cognitive and optical manifestations of fatigue and discomfort. Another section is devoted to different sources of visual fatigue and discomfort, in connection with binocular vision. The chapter considers the problems posed by 3D technologies and content. The whole of the 3D chain, from capture to viewing, via data representation, compression, transmission and display, requires careful mastery in order to limit stereoscopic faults and reproduce content in a suitable manner. The best compromise should be obtained between the quantity or intensity of 3D effects and the level of visual fatigue and discomfort experienced by the majority of people.