Prior research has found that toddlers will form enduring artifact categories after direct exposure to an adult using a novel tool. Four studies explored whether 2- (N = 48) and 3-year-olds (N = 32) demonstrate this same capacity when learning by eavesdropping. After surreptitiously observing an adult use 1 of 2 artifacts to operate a bell via a monitor, 3-year-olds returned to the demonstrated kind of tool as "for" the task and avoided it for an alternative task over 2 days. Two-year-olds performed similarly after eavesdropping on someone with more discriminable artifacts via the method of a window rather than a monitor. These results demonstrate that toddlers can acquire enduring artifact categories after less than 40 s of surreptitious observation. (Contains 3 tables and 2 figures.)