This book constitutes the refereed proceedings of the ACM/IFIP/USENIX 8th International Middleware Conference 2007, held in Newport Beach, CA, USA, in November 2007. The 22 revised full papers presented were carefully reviewed and selected from 108 submissions. The papers are organized in topical sections on component-based middleware, mobile and ubiquitous computing, grid and cluster computing, enhancing communication, resource management, reliability and fault tolerance.