Intelligence and Security Informatics (ISI) can be broadly defined as the study of the development and use of advanced information technologies and systems for national and international security-related applications. The First and Second Symposiums on ISI were held in Tucson, Arizona, in 2003 and 2004, respectively. In 2005, the IEEE International Conference on ISI was held in Atlanta, Georgia. These ISI conferences have brought together academic researchers, law enforcement and intelligence experts, information technology consultant and practitioners to discuss their research and practice related to various ISI topics including ISI data management, data and text mining for ISI applications, terrorism informatics, deception detection, terrorist and criminal social network analysis, crime analysis, monitoring and surveillance, policy studies and evaluation, information assurance, among others. We continue this stream of ISI conferences by organizing the Workshop on Intelligence and Security Informatics (WISI'06) in conjunction with the Pacific Asia Conference on Knowledge Discovery and Data Mining (PAKDD'06). WISI'06 will provide a stimulating forum for ISI researchers in Pacific Asia and other regions of the world to exchange ideas and report research progress. The workshop also welcomes contributions dealing with ISI challenges specific to the Pacific Asian region. Accepted WISI'06 papers will be published along with accepted papers from other workshops in PAKDD'06 in the Springer Lecture Notes in Computer Science (LNCS) series.