StumbleUpon helps you discover and share great websites. As you click Stumble!, we deliver high-quality pages matched to your personal preferences. These pages have been explicitly recommended by your friends or one of over 15 million other websurfers with interests similar to you. Rating these sites you like () automatically shares them with like-minded people - and helps you discover great sites your friends recommend. Using a combination of human opinions and machine learning to immediately deliver relevant content, StumbleUpon presents only web sites that have been suggested by other like-minded Stumblers. Each time the 'Stumble' button is clicked, the user is presented with a high quality web site based on the collective opinions of other like-minded web surfers. StumbleUpon offers nearly 500 topics which users may choose to indicate their interests and preferences so each Stumble produces only the most relevant content. StumbleUpon delivers increasingly relevant content as the Toolbar learns what the user has liked in the past and continues to present quality web sites in the future.