We are pleased to present the proceedings of the 2004 SIAM International Conference on Data Mining. The pervasiveness of data mining in research and industry continues to grow, especially in disciplines such as bioinformatics and homeland security. We were excited to have a record number of paper submissions (161) this year as well as a record number of program committee members (90). We hope that the research and experiences captured in these proceedings are insightful to both expert and novice users and practitioners of data mining approaches.