This document discusses social bookmarking and the social bookmarking site StumbleUpon. It defines social bookmarking as a method for internet users to organize and manage bookmarks of web pages. It describes StumbleUpon as a popular social bookmarking site that allows users to browse websites on topics they select and "stumble" from one site to another. The document provides screenshots and descriptions of features of StumbleUpon like user profiles, interests, and sharing bookmarks.