Welcome to SDM 2012 -- The Twelfth SIAM International Conference on Data Mining, held in Anaheim, CA, home of Disneyland! SDM-2012 continues the series of conferences focusing on the theory and practice of data mining as applied to large data sets in science, engineering, biomedicine, and the social sciences, among others. The conference has a rich program; in addition to strong technical papers, there is also a broad set of tutorials, workshops and mini-symposia. Building on the success of the doctoral forum held in previous years, this year will see a continuation of this popular event. The strong program is also complemented by four keynote talks by renowned researchers from academia and industry: Noshir Contractor from Northwestern, Susan Dumais from Microsoft Research, R. Bharat Rao from Siemens Healthcare, and Qiang Yang from HKUST, Hong Kong, who will share their experiences and wisdom with us. A major conference like SDM is not possible without a team of dedicated people who volunteer their time and effort to serve the community. We would like to thank the entire organizing committee for the excellent job that they have done putting together a strong technical program. Special thanks go to the program co-chairs, Ian Davidson and Carlotta Domeniconi. They recruited the area chairs and the program committee, guided the papers submitted through a thorough and high-standard review process, worked with the reviewers to find the highest quality submissions. We also thank Nitin Agarwal for serving as publicity chair; Jennifer Dy and Jimeng Sun for attracting corporate and government sponsorship to support the event; Nitesh Chawla for putting together a strong tutorial program; Rui Kuang and Chandan Reddy for attracting and identifying a strong set of workshops to complement the main conference program; Yan Liu, who single-handedly served as the local arrangements chair; and the doctoral forum organizers: Jennifer Dy, Yan Liu, and Jimeng Sun. We also thank the tutor