Since the commercialization of the Internet in the 1990s, online retailing has increased steadily. According to the most recent Department of Commerce Census Bureau report,1 retail e-commerce sales in the first quarter of 2004 were $15.5 billion, up 28.1% from the first quarter of 2003. E-commerce sales in the first quarter of 2004 accounted for 1.9% of total sales, compared with 1.6% of total sales for the first quarter of 2003. An important trend in this growth in B2C (business-to-consumer) e-commerce is the participation of small business on the Web. Considering that in the United States small business comprises more than 99% of employer firms,2 this trend is significant. Though the Web offers huge potential to these small businesses for growth and prosperity, and also offers them a very low entry cost, Web visibility becomes the major barrier for them. Small businesses often have difficulty putting up enough funding to compete with brand-name businesses in promotion. So small businesses are desperately in need of a less costly channel for increasing their Web visibility. In the past 4 years and especially since the economic slowdown in 2000, comparison shopping has become more and more popular among online shoppers. Because of the low cost of being listed on comparison-shopping Web sites and the relatively high conversion rate for online shoppers who use comparison shopping, many small businesses found this an ideal channel to increase their Web visibility. As a result, many early participating small businesses gained a customer base in the competition by displaying their products and service prices on comparison-shopping Web sites. Now, it is more and more clear that comparison shopping provides a unique opportunity for small businesses to reach a large customer population with relatively little cost. To help readers better understand this phenomenon, we give a comprehensive introduction to comparison-shopping agents and summarize recent research on their impact in e-commerce.