Within the scope of todays globalisation, linguistic diversity is a given fact of the world we live in. In several educational contexts in Europe, language awareness (LA) activities have been introduced with the objective to prepare pupils cognitively, socially and/or critically for life as multilingual, open minded and/or empowered citizens in a diverse world. Despite previous research in various contexts, the concept of LA remains problematic: a generally accepted, evidence-based conceptualisation is missing. This confronts both research and education with a challenge: in order to develop LA activities, implement them successfully in educational contexts and achieve the expected outcomes, we should know what the concept stands for, how it works and why we would choose to implement it in classrooms (or not). This volume focuses on three apparent simple questions: what, how and why? The first question what? refers to the concept(ual mess) of LA. The second question how? refers to the implementation of LA activities in several educational contexts. The third question why? is a recurrent theme running through all the chapters and deals with a reflection on the way we deal (un)consciously with LA activities in education.