This book describes and evaluates the usefulness of a recently developed lexicographical hybrid: the encyclopedic learner's dictionary (ELD). First, the ELD is analysed from a typological perspective. Two encyclopedic learners' dictionaries are dissected and compared, and a checklist of ELD design features is drawn up. A survey of previous user-based studies is then provided, followed by a description of the questionnaire-based methodology used in this user-centred investigation. Next, a critical analysis of each ELD design feature is provided. Finally, the implications of this research for the future production of ELDs are presented as a checklist of recommendations.