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, wherein the item categorization service is in communication with the data store and the network-based service, and wherein the item categorization service is adapted to: assign a first category to the item of interest by: identifying a plurality of first category candidates based at least in part upon a relevance value associated with the item information and one or more of the categories for items stored by the data store, wherein at least a portion of the first category candidates are hierarchically organized; determining which of the first category candidates has the most first category candidate attributes of the first category candidates; and selecting the first category candidate that has the most first category candidate attributes as the first category of the item of interest; and assign a second category to the item of interest by: determining one or more rules associated with the first category of the item of interest; identifying a plurality of second category candidates using the rules; and selecting a second category of the item of interest from the plurality of second category candidates.