Unlike most traditional media, the Internet is both digital and interactive. Here we do not simply refer to interactions between consumers and a Web site or e-mail, but also between the marketer and the firm’s Web site or e-mail. Furthermore, the digital nature of the Internet records every interaction. These two characteristics — interactivity and digitization — facilitate research possibilities that would be cumbersome and costly using earlier media such as print, radio and television. On the Internet, marketers receive instant feedback on any tactical decision in the form of server log data. We believe that due to technical hurdles, both practitioners and academics under-utilize this omnipresent data residing in server log files. This is unfortunate for practitioners because their online efforts are far less efficient and effective than they could be. This is also unfortunate for academics because even small sites can generate massive amounts of rich data in relatively short times. This chapter introduces readers to server log files and how the basic information in these files helps management achieve goals for their Web sites and e-mail communication. Next, the chapter uses examples to illustrate how server log files make running online experiments easier than one would expect. The chapter closes with a call for more use of server log files in interdisciplinary research, and collaboration between industry and academia.