A custom dictionary is generated for an e-book. A dictionary management system receives a custom dictionary request from a user client operated by a user, the custom dictionary request identifying the e-book and including dictionary management information describing the user. The dictionary management system chooses a group reader profile that has an associated group reading score for the user based on the dictionary management information and candidate words are identified in the identified e-book for inclusion in the custom dictionary. The dictionary management system selects words for inclusion in the custom dictionary from among the candidate words responsive to the associated group reading score for the chosen group reading profile. The dictionary management system generates the custom dictionary using the selected words, and provides the generated custom dictionary to the user client