Research on German as a second language and multilingualism embraces a wide range of themes and issues that are investigated by various disciplines. Choices of research methodology here depend on research questions and theoretical framework conditions. In keeping with the diversity of issues and approaches, research on second language acquisition can employ a broad spectrum of methodological procedures. This volume addresses highly diverse empirical methods, the advantages and limitations of which are described by the authors with reference to concrete research projects. In this way the volume aims to provide insights into research on second language acquisitions in a multilingual society and to offer suggestions for further research projects.