Development of Tumblr began in 2006 during a two-week gap between contracts at David Karp's software consulting company, Davidville (housed at Karp's former internship with producer-incubator Fred Seibert's Frederator Studios, which was located a block from Tumblr's current headquarters).
Karp had been interested in tumblelogs (short-form blogs) for some time and was waiting for one of the established blogging platforms to introduce their own tumblelogging platform.
In 2013, Tumblr began allowing companies to pay to promote their own posts to a larger audience.
On November 10, 2015, Tumblr introduced an integrated instant messaging function, allowing users to chat between other Tumblr users.
The feature is being rolled out in a "viral" manner; it was initially made available to a group of 1500 users; other users may receive access to the messaging system if they are sent a message by any user that has received access to the system itself.
However, an analysis conducted by news and technology site Tech Crunch has shown that over 22% of all traffic in and out of Tumblr is classified as pornography.
In addition, a reported 16.45% of blogs on Tumblr exclusively contain porn.
As no one had done so after a year of waiting, Karp and developer Marco Arment began working on their own tumblelogging platform.
In early June 2012, Tumblr featured its first major brand advertising campaign in conjunction with Adidas.The government shortly reversed its decision to block the site and said it had asked Tumblr to self-censor its pornographic content.The suicide of a British teenager, Tallulah Wilson, raised the issue of suicide and self-harm promotion on Tumblr as Wilson was reported to have maintained a self-harm blog on the site.The change was intended to improve the legibility of reblogs, especially on mobile platforms, and complements the inability to edit existing comments.Although some users had requested such a change to combat posts made illegible by extremely large numbers of comments on a reblogged post, the majority of users (even those who had requested such a change) criticized the new format.The site became available to Black Berry smartphones on April 17, 2010, via a Mobelux application in Black Berry World.