Multilingualism is broadly understood as the knowledge and use of two or more languages by individuals in their everyday lives, both private and professional. It is increasingly acknowledged as an important issue of the contemporary world and the interest in the matter of multilingualism is growing rapidly in many areas, such as research, politics, or education. The authors of this book combine some of the questions in a truly interdisciplinary perspective in order to provide an insight into the variety and diversity of research problems of multilingualism. This collection is divided into ten chapters considering the selected matters from different points of view, gathering together empirical research from various fields.