Vocabulary annotations on the margin of a text have been used for centuries to facilitate reading comprehension. In foreign language teaching, such glosses have also been used for teaching specific vocabulary. Since the advent of hypertext, glosses in electronic form have allowed for greater flexibility and interactivity. Electronic glosses have the inherent advantage of being invisible until the learner opens them, thus requiring a conscious effort on the part of the learner. This supports learning because new words are best retained when learners have to take an active approach to finding out word meanings and are given opportunities for using them in context. In a longitudinal study it was found that learners regard tailor-made electronically-glossed reading tasks as helpful and motivating. This book introduces an effective and motivating method for facilitating vocabulary acquisition that is particularly suitable for teaching languages for specific purposes but can equally well be adapted for general language courses.