The fourth international workshop on Mining Complex Data follows the three previous editions in 2005 in conjunction with IEEE ICDM 2005, Huston, USA, in 2006 in conjunction with IEEE ICDM 2006, Hong-Kong, China, and in 2007 in conjunction with ECML/PKDD 2007, Warsaw, Poland. The post-proceedings of the last workshop have been published by Springer in LNAI (Vol. 4944).

MCD 2008 builds on the success of the previous editions to bring new ideas and research fields to the area of mining complex data. These previous editions met perfectly the organizing committee expectations. This was due to the number of submissions from different countries, the high quality of presentations, and, finally, the large assistance. We would like to reproduce and reinforce this experience this year in order to allow for a large number of researchers to explore new ideas in the area of mining complex data.