How can I unjoin a group on Facebook?

[MimesHEATâ„¢]

To unjoin a group on facebook, all you have to do is go to the groups page (you can do this by going to your profile, clicking info, scrolling down to groups, and click on the desired group) and clicking on the button that says 'leave group'.
That simple! (:

[Jess R]

If you open your HOME page (when you first log in) you'll see "applications" in the right-hand column. Click on the "groups" application, then go to "My Groups" in the top left. You'll see a list of groups which you are a member of. When you find a group you'd like to leave, go to it, and select the "leave group" option (it is on the right side, the third link down from the group's picture).