Every year we witness acceleration in the availability, deployment, and use of distributed applications. However building increasingly sophisticated applications for extant and emerging networked systems continues to be challenging for several reasons: – Abstract models of computation used in distributed systems research often do not fully capture the limitations and the unpredictable nature of realistic distributed computing platforms; – Fault-tolerance and ef?ciency of computation are dif?cult to combine when the c- puting medium is subject to changes, asynchrony, and failures; – Middleware used for constructing distributed software does not provide services most suitable for sophisticated distributed applications; – Middleware services are speci?ed informally and without precise guarantees of e- ciency, fault-tolerance, scalability, and compositionality; – Speci?cation of distributed deployment of software systems is often left out of the development process; – Finally, there persists an organizational and cultural gap between engineering groups developing systems in a commercial enterprise, and research groups advancing the scienti?c state-of-the-art in academic and industrial settings. The objectives of this book are: (1) to serve as a motivation for de?ning future research programs in distributed computing, (2) to help identify areas where practitioners and engineers on the one hand and scientists and researchers on the other can improve the state of distributed computing through synergistic efforts, and (3) to motivate graduate students interested in entering the exciting research ?eld of distributed computing.