Pattern classification is a very general concept with numerous applications ranging from science, engineering, target marketing, medical diagnosis, and electronic commerce to weather forecast based on satellite imagery. A typical application of pattern classification is mass mailing for marketing. For example, credit card companies often mail solicitations to consumers. Naturally, they would like to target those consumers who are most likely to respond. Often, demographic information is available for those who have responded previously to such solicitations, and this information may be used in order to target the most likely respondents. Another application is electronic commerce of the new economy. E-commerce provides a rich environment to advance the state of the art in classification, because it demands effective means for text classification in order to make rapid product and market recommendations.