This book is about foreign language learning in non-formal Online Tandems. The collected papers by contributors who have expertise in the field of Language Pedagogy and Foreign Language Acquisition gather information on online interactions, such as the initiation of tandems, the mentoring of online activities and learners' interaction, as well as the assessment of the processes at hand. The handbook targets stakeholders, institutions of higher education, language teachers and tandem trainers at educational institutions that want to set up Online Tandems especially designed for third language learners. The book is the result of the three-year project L3TASK carried out at five universities in Austria (Wien), Germany (Jena) and Spain (Alicante, Barcelona, Madrid) and associated partner institutions in China. It was funded by the European Commission in the frame of the Life Long Learning Programme.