Due to the simplicity, attractiveness and effectiveness for collaborative authoring and knowledge management, wikis are now massively disseminated and used in different domains. This workshop focuses on wikis for the specific domain of software engineering. It aims at bringing together researchers, practitioners, and enthusiasts interested on researching, exploring and learning how wikis can be improved, customized and used to better support software engineering. Based on lessons learned and obstacles identified, a research agenda will be defined with key opportunities and challenges. This edition at WikiSym’2009 follows others at ICSE’2009, WikiSym’2008 and WikiSym’2007. Categories and Subject Descriptors D.2.6 [Software Engineering]: Programming Environments; I.7.2 [Document And Text Processing]: Document Preparation—Hypertext/Hypermedia, Markup Languages General Terms Wikis for software engineering Keywords Wikis, software development, collaboration, documentation.