With the growing ubiquity of computing systems, it is essential that we can rely on the services they deliver. Justifying reliance in computer systems requires scientific techniques to derive evidence from given systems or predict such evidence. This tutorial book gives an overview of the current state of the art in measuring the different aspects of dependability of systems: reliability, security and performance. The main impulse for this dependability metrics project resulted from a research seminar, held at Schloss Dagstuhl, Germany, in October/November 2005. The 25 chapters, based on the outcome of the research seminar, are organized in five parts on foundations, reliability metrics, security metrics, performance metrics, and overlapping metrics. The final part shows that only a combined consideration of important dependability attributes will lead to the design objective: the development of systems we can really trust.