Web site usability is concerned with how easy and intuitive it is for individuals to presence, as perceived by users. The usability of Web sites is important because high usability is associated with a positive attitude and greater trust towards the Web site. Poorly designed Web sites with low usability lead to negative financial impacts. Existing approaches to Web site usability include measurement and tracking of parameters such as response time and task completion time, and software engineering approaches that specify general usability guidelines and common practices during software development. This chapter analyzes usability from the point of view of Web site design parameters. An analysis of usability and other design characteristics of 200 Web sites of different kinds revealed that design aspects such as information content, ease of navigation, download delay, and Web site availability positively influence usability. Web site security and customization were not found to influence usability. The chapter explains these results and suggests design strategies for increasing Web site usability.