Social bookmarking is a way to share interesting links with others. Sites like Digg, StumbleUpon, and Delicious allow you to vote for links; other users can often see which links you voted for.

Blogging is a much broader concept. In basic terms, a weblog (blog) entry is most often a diary or news update, depending on whether it’s a personal or professional site. Sites like Blogger and WordPress allow for the easy creation of blogs.

A wiki is a site where all users can actively edit the content of a webpage.

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How are they similar? Well, they all encourage the active participation of internet users and wouldn’t even exist if it weren’t for the users.

How are they different? See above.