This volume contains the proceedings of UIC 2008, the 5th International C- ference on Ubiquitous Intelligence and Computing: Building Smart Worlds in Real and Cyber Spaces. The conference was held in Oslo, Norway, during June 23–25, 2008. The event was the fifth meeting of this conference series. USW 2005 (First International Workshop on Ubiquitous Smart World), held in March 2005 in Taiwan, was the first event in the series. This event was followed by UISW 2005 (Second International Symposiumon Ubiquitous Intelligence and Smart Worlds) held in December 2005 in Japan, by UIC 2006 (Third International Conference on Ubiquitous Intelligence and Computing: Building Smart Worlds in Real and Cyber Spaces) held in September 2006 in Wuhan and Three Gorges, China, and by UIC 2007 held in July 2007 in Hong Kong. Ubiquitous computers, networks and information are paving the road to a smart world in which computational intelligence is distributed throughout the physical environment to provide trustworthy and relevant services to people.