The International Conference on Mobile and Ubiquitous Multimedia (MUM) is a leading annual international conference, which provides a forum for presenting the latest research results on mobile and ubiquitous multimedia. The conference brings together experts from both academia and industry for a fruitful exchange of ideas and discussion on future challenges, in a comfortable and effective single-track conference format. The 12th International Conference on Mobile and Ubiquitous Multimedia (MUM 2013) will be held in Luleå, Sweden, December 2-5, 2013. It is organized by the Pervasive and Mobile Computing Group, of the Department of Computer Science, Electrical and Space Engineering of Luleå University of Technology, in cooperation with ACM SIGCHI. In addition to the peer-reviewed accepted papers, the conference program will include keynote presentations, posters, demos and an industry track. The conference will also have co-located workshops. The technical program will be complemented by several social events to facilitate informal discussions and networking among the conference attendees and invited guests. A Best Paper Award and Best Student Paper Award will be awarded during the conference dinner for outstanding contributions.