This study investigates the importance of object function (action-object-outcome relations) on object individuation in infancy. Five experiments examined the ability of 9.5- and 12-month-old infants to individuate simple geometric objects in a manual search design. Experiments 1 through 4 (12-month-olds, N = 128) provided several combinations of simple appearance-function relations defined by changes in form and color (appearance) or objects' ability to make a rattling sound when shaken (function). Only when object function covaried with the appearance differences (Experience 3) were infants able to individuate, suggesting that object function played a facilitating but not a determining role. In Experiment 5, 9.5-month-olds (N = 32) were unable to demonstrate such function-facilitated individuation, suggesting that this ability develops between the age of 9.5 and 12 months. (Contains 3 figures.)