The Ubiquitous Computing conference series provides the premier forum in which to present original research results in all areas relating to the design, implementation, app- cation and evaluation of ubiquitous computing technologies. It is a well-established platform to introduce and discuss research that enables new capabilities, appropriate security and privacy, improved user experiences and simplified and powerful devel- ment and deployment practices. These proceedings contain the papers presented at the Ninth International Conf- ence on Ubiquitous Computing (UbiComp 2007) in Innsbruck, Austria, in September 2007. Our call for papers resulted in 150 submissions, each of which was assigned to a primary and a secondary member of our Program Committee. Every primary and secondary member was responsible for assigning one or more additional qualified reviewers with specific expertise in the field. After double-blind reviews and an online discussion, we had a two-day face-to-face meeting with 38 of the 40 Program C- mittee members attending the PC meeting held just before the Pervasive 2007 conf- ence in Toronto, Canada, in May 2007. We are grateful to Khai Truong , Jeremy Knight and Alex Varshavsky of the University of Toronto for providing facilities and support for this meeting. At the PC meeting, about 80 of the submissions were in- vidually and extensively discussed in one of the three subgroups sensors, experiences and systems as well as in the calibration and decision panels. The PC finally selected 29 papers for publication in these proceedings.