The purposeofthis book is to providea recordofthe stateofthe art in
Topic Detection and Tracking (TDT) in a single place. Research in TDT
has been going on for about five years, and publications related to it
are scattered all over the place as technical reports, unpublished
manuscripts, or in numerous conference proceedings. The third and fourth
in a series of on-going TDT evaluations marked a turning point in the
research. As such. it provides an excellent time to pause. review the
state of the art. gather lessons learned, and describe the open
challenges. This book is a collection oftechnical papers. As such, its
primary audience is researchers interested in the the current state of
TDT research, researchers who hope to leverage that work sothat theirown
efforts can avoid pointlessdu- plication and false starts. It might also
pointthem in the direction ofinteresting unsolved problems within the
area. The book is also of interest to practition- ers in fields that are
related to TDT--e.g., Information Retrieval. Automatic Speech
Recognition. Machine Learning, Information Extraction, and so on. In
thosecases, TDTmay provide arich application domain for theirown
research, or it might address similarenough problems that some lessons
learned can be tweaked slightly to answer-perhaps partiallY-