This book constitutes the proceedings of the 15th European Conference on Technology Enhanced Learning, EC-TEL 2020, held in Heidelberg, Germany, in September 2020. The 24 research papers and 20 demo and 5 poster papers presented in this volume were carefully reviewed and selected from 91 submissions. The European Conference on Technology-Enhance Learning, which celebrates its 15th anniversary this year, is committed to address global challenges and quality education. The papers deal with the Sustainable Development Goals, particularly SDG 4 and SDG 10, to help to reduce the existing gaps and inequalities between countries and regions from around the world in terms of inclusiveness, equity, access, and quality of education. The chapters: "Designing an Online Self-Assessment for Informed Study Decisions: The User Perspective"; "Living with Learning Difficulties: Two Case Studies Exploring the Relationship Between Emotion and Performance in Students With Learning Difficulties"; "Applying Instructional Design Principles on Augmented Reality Cards for Computer Science Education"; and "Teaching Simulation Literacy With Evacuations - Concept, Technology, and Material for a Novel Approach" are available open access under a Creative Commons Attribution 4.0 International License via link.springer.com. Due to the Corona pandemic EC-TEL 2020 was held as an virtual event.

This book constitutes the proceedings of the 26th International Conference on Collaboration Technologies and Social Computing, CollabTech 2020. The conference was scheduled to take place in Tartu, Estonia, in September 2020. It was held virtually due to the COVID-19 pandemic. The 10 full and 5 work-in-progress papers presented in this volume were carefully reviewed and selected from 25 submissions.