When considering intelligence it is worth remembering that a large proportion of the human brain is devoted to sensory input. In insect brains the proportion is even greater – often exceeding 90% of the total operational cells. Sensing the world therefore has a huge impact on intelligence. Without input how can an entity perceive the world, respond, learn or communicate? The nature of the sensory input dictates the nature of the entity. In this chapter we consider how sensory input is dealt with in machine systems. We look here at the processes involved in computer vision and other sensing systems such as audio, ultrasonics, infrared and radar.