Book excerpt: This book constitutes the refereed proceedings of the 4th International Conference on Ubiquitous Intelligence and Computing, UIC 2007, held in Hong Kong, China in July 2007, co-located with ATC 2007, the 4th International Conference on Autonomic and Trusted Computing. The 119 revised full papers presented together with 1 keynote paper and 1 invited paper were carefully reviewed and selected from 463 submissions. The papers are organized in topical sections on smart objects and embedded systems, smart spaces/environments/services, ad-hoc and intelligent networks, sensor networks, pervasive communication and mobile systems, context-aware applications and systems, service oriented middleware and applications, intelligent computing: models and services, as well as security, safety and privacy.