Nine experiments examined 6- to 10-month-olds' formation of an abstract category representation for "between." Findings indicated that older, but not younger infants, could form an abstract category representation for "between" when performing in an object-variation version of the between categorization task. Six- to 7-month-olds could form category representations for "between" in the object-variation version of the between categorization task; such representations were specific to the particular objects presented. (Author/KB)