The International Workshop on Principles of Diagnosis (DX) is an annual event that started in 1989 and is rooted in the Artificial Intelligence (AI) community. This annual international workshop has been uniting researchers and practitioners with diverse backgrounds (Artificial Intelligence (AI), verification, software engineering, debugging, ...) in order to leverage research in the global context of diagnosis, that is, identifying the root causes for encountered issues. The DX Workshop series has been offering a forum to present current research and experience reports, exchange and discuss emerging ideas, as well as debate current issues and envisioned future challenges. Papers presented at the workshop cover a variety of theories, principles, and computational techniques for diagnosis, monitoring, testing, reconfiguration, fault- adaptive control, and repair of complex systems. Applications of these theories, principles, and techniques to industry-related disciplines and other real-world problems are also important topics of the workshop. Like the previous workshops in this series, DX-2015 encourages the interactions and the exchange of theories, techniques, applications, and experiences amongst researchers and practitioners from diverse backgrounds – artificial intelligence, control theory, verification, software and systems engineering, and other related areas – who share an interest in different aspects of diagnosis, and the related fields of testing, reconfiguration, maintenance, prognosis, and fault-adaptive control. DX is a lively forum that has traditionally adopted a single track program with a limited number of participants in order to promote detailed technical exchange and debate while at the same time making efforts to develop synergistic approaches to solving real-world problems.