This volume focuses on computer- and digitally-assisted language learning in all of its forms: technology-enhanced language learning, network-based language learning, mobile-assisted language learning and so on, in close relation to the topic of sustainability. How can these technologies and techniques be implemented in a sustainable and repeatable way? The book covers a wide range of areas in terms of this "sustainability". These include: (1) education (teacher/learner training) (2) normalisation (integration) (3) systems (reliability, support, development) (4) mobility (mobile-assisted language leaning) (5) innovation (trends, research) The volume samples research and practice in CALL from around the world, organised into sections. It has an introduction and a conclusion written by the editors (Ana Gimeno, Mike Levy, Françoise Blin and David Barr) which covers the state of the art at the moment and directions it is likely to take in the future. The Fourth WorldCALL conference marks two important aspects of the original inspiration for this truly worldwide, truly humanistic forum. This volume of carefully curated conference papers amply demonstrates CALL's proven Sustainability, after 3 decades of initially somewhat bumpy progress. The sheer range of this valuable book's topics, technologies and practitioners from the technical have-countries to the technically less wealthy, also proves that CALL is a great motivator, for teachers and learners across the planet. I recommend it as a rich resource for specialists and curious beginners alike. There is much to enjoy and enrich in these pages.