Wikipedia:Tip of the day/June 2, 2006
If you want to compare the differences between two revisions of a page, click the "history" tab at the top of the page, then select two checkboxes to mark the revisions which you want to compare. Alternatively, click the "cur" link to see the differences between a revision and the current (most up-to-date) revision, or the "last" link to see the differences between a revision and the previous one. You'll see two columns of text next to each other, with any changes in red. You can also view the drafts on their own from that page, or change which versions you are comparing. Just be aware that changing templates and images are not recorded.
Read more: Wikipedia:Page history