Charles Clarke is an Associate Professor in the David R. Cheriton School of Computer Science at the University of Waterloo. He has published on a wide range of topics within the area of information retrieval, including papers related to evaluation, efficiency, ranking, question answering, document structure, and XML. He was a Program Co-Chair of SIGIR 2007, and he was the General Co-Chair of SIGIR 2003. From 2004 to 2006 he was the coordinator of the Terabyte Retrieval track at TREC, which examined efficiency and scalability issues. Prior to joining the University of Waterloo in 1999, he was an Assistant Professor in the Department of Electrical and Computer Engineering at the University of Toronto. He has previously held software development positions at a number of computer consulting and engineering firms. In 2006 he spent a sabbatical at MSN, where he was involved in the development of the Windows Live search engine.