Book excerpt: This book constitutes revised selected papers from the workshops held at the 27th International Conference on Parallel and Distributed Computing, Euro-Par 2021, which took place in Portugal, in August 2021. The workshops were held virtually due to the coronavirus pandemic. The 39 full papers presented in this volume were carefully reviewed and selected from numerous submissions. The papers cover all aspects of parallel and distributed processing. These range from theory to practice, from small to the largest parallel and distributed systems and infrastructures, from fundamental computational problems to full-edged applications, from architecture, compiler, language and interface design and implementation to tools, support infrastructures, and application performance aspects.