Customer relationship management (CRM) is a concept for increasing companies’ profitability by enabling them to identify and concentrate on their profitable customers. The term “electronic commerce customer relationship management” (ECCRM) refers to the application of CRM in electronic commerce, i.e., when business relationships are maintained via the Internet or World Wide Web. Previous studies on the effectiveness of ECCRM have often focused on the process level, technical aspects, or on marketing issues. Yet only little evidence has been reported for the impact of ECCRM on the company level. In this chapter we present the results from a large-scale empirical study investigating the impact of ECCRM on corporate success in electronic commerce. The study comprises 469 cases of general companies in the German-speaking market. We find that ECCRM is a critical success factor in electronic commerce, independent of companies’ time on the Web. It is especially critical for B2C and small companies.