This book takes up the subject of dictionary use from the perspective of advanced learners. The study investigates the effects of the use of a monolingual learner's dictionary on students' performance in a complex comprehension task of interpreting texts with modified idioms. The major, empirical part reports on an experiment, which was an attempt to analyse comprehension scores in the light of the consultation process. The results reveal a mildly positive influence of the monolingual dictionary on reading comprehension.