This paper investigates whether a search engine's ordering of algorithmic results has an important effect on website traffic. A website's ranking on a search engine results page is positively correlated with the clicks that it receives. This could result from the search engine's accurately predicting the websites relevance to users. Or it could result from users merely clicking on the highest ranked links, regardless of the website's relevance. Using a unique dataset, we find that a website's rank, not just The analysis for this paper was performed in conjunction with ongoing work for Microsoft Corporation; Keystone and Seabright acknowledge financial support from Microsoft. The primary data that were used in the analysis come from log files from Microsoft's Bing search engine and include the website names, search result rankings, and click-through rates for results that were presented in response to user search queries on Bing.com. Supplementary data for additional website click-through rates were derived from additional Microsoft opt-in consumer panel data that contained online behavior. The authors are grateful to Elan Fuld, who provided excellent research assistance; to Scott Gingold, who was involved with the project from the beginning and gave us invaluable feedback, ideas, encouragement and support; and to Thierry Magnac, who gave us invaluable econometric expertise and spent much time helping us to understand the data.M. Glick Department of Economics, University of Utah, Salt Lake City, UT 84112, USA e-mail: glick@economics.utah.edu its relevance, strongly and significantly affects the likelihood of a click. We also find evidence that rank influences CTRs partly by controlling access to the scarce attention of users, but primarily by substituting the reputational capital of the search engine for the reputation of individual websites.