Mayer, MatthiasBederson, Benjamin B.We have implemented a task and session based visual web history tool called Browsing Icons that dynamically draws animated graphs of the user's paths through the web. Using a proxy, it can be attached to any common web browser. Every web session builds an individual Browsing Graph with a characteristic shape. The graphs are organized in a hierarchy of user-defined tasks. Users can interrupt tasks and continue later using the graphs that provide access to all the web pages they have visited so far. The graphs can be reused for similar or recurrent tasks. By clustering the history hierarchically according to tasks, we try to cope with scale and to provide a powerful concept for easy revisitation. The visualizations have been implemented using the Jazz framework for zoomable user interfaces (ZUIs) in Java. A usability study showed that users like the system very much and appreciate its support of revisiting web pages. Ten users revisited web pages after a few minutes and other web pages after one to six days using both Netscape with Browsing Icons and Netscape alone. With the tool they completed the short-term revisits in 84% of the time required when using Netscape alone. The revisits after one to six days users could accomplish in 57.8% of the time they needed when using Netscape, thereby visiting only 53.8% as many pages. Users were significantly more satisfied with Browsing Icons than with pure Netscape. KEYWORDS: Web History Visualization, Task Based Information Organization, Information Visualization, Web Browser Usability, Jazz. UMIACS-TR-2001-85 HCIL-TR-2001-19en-USTechnical Report