You'll see ads on Tumblrs from time to time. There are two different types: Ads we run, and ads run by the blog owner.
Tumblr's On-Blog Ads
Tumblr runs ads from a variety of providers. To learn more about how we source our ads, check out this article.
We currently run ads in the blog view* on web. It's not possible to opt-out of this right now.
*Blog view (formerly known as peepr) is the in-dashboard view of a blog.
We do not serve ads on the blog network (yoururl.tumblr.com). If you're using Tumblr on web and you see ads on a web-facing blog, those are run by the blog owner.
In the Apps
We run ads on blog pages in the mobile apps. It's not possible to opt out of this right now.
Third Party Ads
You're welcome to use third party ads on your blog. However, before doing so please consult our Community Guidelines, specifically the section on spam:
Don't use deceptive means to generate revenue or traffic, or create blogs with the primary purpose of affiliate marketing.
If you encounter sketchy third party ads, you can report the blog or post in question.