This book constitutes the refereed proceedings of the Third Usability Symposium of the Human-Computer Interaction and Usability Engineering Workgroup of the Austrian Computer Society, USAB 2007, held in Graz, Austria, in November 2007. The 21 revised full papers and 18 revised short papers presented together with one poster paper and one tutorial were carefully reviewed and selected from 97 submissions during two rounds of reviewing and improvement.