At WordPress.com, we sometimes display advertisements on your blog to help pay the bills. This keeps free features free!
To eliminate ads on your blog entirely, you can purchase our WordPress.com Premium or WordPress.com Business plans. This is especially attractive and useful to business blogs in order to eliminate any possibility of competitors’ ads displaying on their domains.
Note: VIP and WordAds users/blogs are able to run their own ads, but standard accounts are not. See this page on advertising for more information on running ads on your blog. In addition, this does not remove the WordPress.com footer credit.