This book provides an in-depth analysis of what happens when intermediate level learners of a foreign language use a bilingual dictionary when writing. Dictionaries are frequently promoted to people learning a foreign language. Nevertheless, teachers often talk about their students' inability to use dictionaries properly, especially when they write, and this can be problematic. This book paints a comprehensive picture of the differences a dictionary makes and brings out the implications for language learning, teaching, and testing practices. It draws on research in which participants in three studies took writing tests in two test conditions - with and without a dictionary. They were also asked what they thought about the two test types. Their performances and opinions were analyzed in a variety of ways. Conclusions from the data highlight some of the practical issues to be kept in mind if we want to help foreign language learners to use bilingual dictionaries effectively when writing.