This special section of the International Journal on Software and Systems Modeling (SoSyM) contains a selection of the best papers accepted at the 17th edition of the international conference series on Formal Aspects of Component Software (FACS). This conference was held online on October 28-29, 2021. The aim of the conference series is to study how formal methods can be applied to component-based software and system development. Component-based software development proposes sound engineering principles and techniques to cope with the complexity of modern software systems. Many challenging conceptual and technological issues remain in component-based software development theory and practice. Furthermore, the advent of service-oriented and cloud computing, cyber-physical systems, and the Internet of Things comes with new challenges, such as quality of service and robustness to withstand faults, which require revisiting established concepts and developing new ones. Formal methods have provided foundations for component-based software through research on mathematical models for components, composition and adaptation, and rigorous approaches to verification, deployment, testing, and certification. After the FACS'21 conference took place, the five best papers were selected, and the authors of these papers were invited to submit a revised and extended version of their work to this special section. After a meticulous review process, we finally accepted three of the five invited papers.