Tumblr (stylized on its home page as tumblr.) is a microblogging and social networking website founded by David Karp in 2007, and owned by Yahoo! since 2013. The service allows users to post multimedia and other content to a short-form blog. Users can follow other users' blogs. Bloggers can also make their blogs private. For bloggers, many of the website's features are accessed from a "dashboard" interface.

As of August 1, 2016, Tumblr hosts over 307.5 million blogs. As of January 2016, the website had 555 million monthly visitors.