1. A system for categorizing items, the system comprising: a data store that stores item information related to a first plurality of items offered for sale using a network-based service; and a computing device having one or more processors, wherein the computing device is configured to operate the network-based service and is in communication with the data store, and wherein the network-based service is operative to: receive a request for a category recommendation for an item of the first plurality of items, the request including first item information associated with the item; and submit the first item information to a categorization service, wherein the categorization service is operative to: generate an item vector from the first item information according to a vector space model; compare the item vector to at least one category vector, wherein the at least one category vector comprises a representation of at least a portion of a textual description of an item category according to the vector space model, wherein the item category is maintained by the network-based service and associated with a second plurality of items; determine the category recommendation to be the item category when a deviation of an angle between the item vector and the at least one category vector is less than a threshold value; and update the first item information to include the item category.