Web site design is critical to the success of electronic commerce and digital government. Effective design requires appropriate evaluation methods and measurement metrics. The current research examines Web site navigability, a fundamental structural aspect of Web site design. We define Web site navigability as the extent to which a visitor can use a Web site’s hyperlink structure to locate target contents successfully in an easy and efficient manner. We propose a systematic Web site navigability evaluation method built on Web mining techniques. To complement the subjective self-reported metrics commonly used by previous research, we develop three objective metrics for measuring Web site navigability on the basis of the Law of Surfing. We illustrate the use of the proposed methods and measurement metrics with two large Web sites.