Intelligence and Security Informatics (ISI) is concerned with the study of the dev- opment and use of advanced information technologies and systems for national, int- national, and societal security-related applications. The annual IEEE International Conference series on ISI was started in 2003 and the first four meetings were held in the United States. In 2006, the Workshop on ISI (http://isi. se. cuhk. edu. hk/2006/) was held in Singapore in conjunction with the Pacific Asia Conference on Knowledge Discovery and Data Mining, with over 100 contributors and participants from all over the world. PAISI 2007 (http://isi. se. cuhk. edu. hk/2007/) was then held in Chengdu, China and PAISI 2008 (http://isi. se. cuhk. edu. hk/2008/) was held in Taiwan. These ISI conferences have brought together academic researchers, law enforcement and intel- gence experts, information technology consultants 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 and intent detection, terrorist and criminal social network analysis, public health and bio-security, crime analysis, cyber-infrastructure protection, transportation infrastructure security, policy studies and evaluation, and information assurance, among others. We continued the stream of ISI conferences by organizing the 2009 Pacific Asia Workshop on ISI (PAISI 2009) in conjunction with the Pacific Asia Conference on Knowledge Disc- ery and Data Mining (PAKDD 2009).