The Common European Framework of Reference for Languages (CEFR) has become the yardstick for teaching and testing language skills in Europe and elsewhere. Yet little is known about the relationships between the communicative levels established using the can-do statements of the CEFR and the developmental stages of grammatical and lexical development described by Second Language Acquisition (SLA) research. This book presents empirical research by members of the SLATE network (Second Language Acquisition and Testing in Europe), aimed at bridging this gap. The studies deal with several target languages, including Dutch, English, Finnish, French, Italian, Norwegian and Spanish, with adult, adolescent and child learners in both formal and informal contexts.