In today's workplace, much information is delivered over the Web, while email remains the workhorse of person-to-person collaboration. Our current mail user agents make it easy to get a web page by clicking on a link in an email, but the reverse link to our email about the web page is missing. To provide this missing link, we developed Sidebar, a plug-in that can run inside both the web browser and the file manager. As the user navigates the Web, or a file system, Sidebar provides a summary of user email that links to the currently displayed document, or folder. In using our software, we've found this basic operation results in many emergent properties that make Sidebar a powerful collaboration tool. Publication Info: Submitted to WWW 2008, 21-25, April 2008 8 Pages