This book presents a key piece of the vision and strategy developed in STELLAR. It sets out a new mid-term agenda by defining Grand Challenges for research and development in technology-enhanced learning. Other than mere technology prizes, STELLAR Grand Challenges deal with problems at the interface of social and technical sciences. They pose problems that can be solved only in interdisciplinary collaboration. The descriptions of the Grand Challenge Problems were sent out to a number of stakeholders from industry, academia, and policy-making who responded with insightful, creative and critical comments bringing in their specific perspectives. This book will inspire everyone interested in TEL and its neighboring disciplines in their future projects. All of the listed problems, first hints with respect to the approach, measurable success indicators and funding sources are outlined. The challenges focus on what noted experts regard as important upcoming, pending, and innovative fields of research, the solution of which is within reach in a timeframe of a mere 2 to 15 years of work.