The effective delivery and presentation of information is critically dependent on understanding the context in which that information is to be used. However, a keyword based approach to defining and managing context has limited effectiveness, e.g. through the prevalence of homonymy and synonymy. Context needs to be defined semantically, specifically in terms of an ontology. This workshop will consider all the research challenges related to representing, managing, using and learning contextual information. Homepage: http://semanticweb.org/wiki/CIAO2009