The nature of the object concept is reviewed al various zoological levels, and special importance is given to the notion of its continued existence. Three fundamentally different types of response to the disappearance of an object are described: (1) on the invertebrate level, stereotyped forms of behavior can either increase or decrease the probability of a further encounter with the same object; (2) certain animais learn to associate a delayed response with the object's disappearance, but never exhibit anticipatory search in a new situation; (3) higher mammals and certain birds immediately adjust their search to relevant spatial-temporal relationships. It is argued that while the members of species which attain object permanence may differ in certain features of their sensorimotor development, their cognitive ontogeny follows the same basic principles.