This book describes and evaluates the usefulness of a recently developed lexicographical hybrid: the encyclopedic learner's dictionary (ELD). It attemps to answer three key questions: i) What are ELDs?, ii) How useful are they?, and iii) How can they be designed to serve their users most effectively? The first chapter analyses the ELD from a typological perspective. First, the elements combined to create this new branch of lexicographical typology are examined. Next, two encyclopedic learners' dictionaries are dissected and compared: The "Longman Dictionary of English Language and Culture" and the "Oxford Advanced Learner's Encyclopedic Dictionary". Each ELD is compared with its non-encyclopedic parent dictionary, and a checklist of ELD-specific design features is drawn up. The second chapter focuses on the user perspective in lexicographical research. First, a critical survey of previous user-based studies is provided. Next, the questionnaire-based methodology used in the investigation is described. Fourty informants completed the questionnaire and an attempt is made to correlate user characteristics with dictionary use and with attitudes towards the inclusion of encyclopedic information in learners' dictionaries. In the third chapter each design feature found in the ELDs is described in depth and the informants' evaluations of its usefulness are supplied. In this manner, the typological focus of the first chapter and the user perspective of the second chapter are synthesized in a user-informed analysis and evaluation of ELD components. Finally, the implications of this research for the future production of ELDs are presented as a checklist of recommendations, and suggestions for future lexicographical research are made.