We present ICARUS, a contextual information retrieval system, which uses the current email message and a multi-tiered user model to retrieve relevant content and make it available in a sidebar widget embedded in the email client. The system employs a dynamic retrieval strategy to conduct automated contextual search across multiple information sources including the user's hard drive, online documents (wikis, blogs and files) and other email messages. It also presents the user with information about the sender of the current message, which varies in detail and degree based on how often the user interacts with this sender. We conducted a formative evaluation which compared three retrieval methods that used different context information: current message plus a multi-tiered user model; current message plus a single-tiered, aggregate user model; and lastly, current message only. Results indicate that the multi-tiered user modeling approach yields better retrieval performance than the other two. In addition, the study suggests that dynamically determining which sources to search, what query parameters to use, and how to filter/re-rank results can further improve the effectiveness of contextual IR. © 2011 ACM.