1. A system for categorizing items, the system comprising: a network-based service configured to: receive a request to categorize an item of interest, the request including item information regarding the item of interest; and transmit the request to an item categorization service; a data store configured to store categories for items, wherein at least a portion of the categories are hierarchically organized with respect to one another; and the item categorization service in communication with the data store and the network-based service, the item categorization service configured to: assign a first category to the item of interest by: determining a plurality of first category candidates based at least in part upon an assessment of the relevance of the item information with one or more first categories stored by the data store; and assigning, as the first category for the item of interest, a first common ancestor of the hierarchically organized first category candidates, the first common ancestor comprising a category that is hierarchically superior to any remaining first category candidates; and assign a second category to the item of interest by: determining a plurality of second category candidates based at least in part upon an assessment of the relevance of the item information with one or more second categories stored by the data store; and assigning, as the second category for the item of interest, a second common ancestor of the hierarchically organized second category candidates, the second common ancestor comprising a category that is hierarchically superior to any remaining second category candidates.