What was the first hashtag ever used on Twitter?

The first hashtag ever used on Twitter was #barcamp. Chris Messina posted it on August 23, 2007, suggesting that the pound sign could organize conversations around groups or events.

Messina drew the idea from Internet Relay Chat, where the # symbol identified chat rooms. His original tweet asked whether users should use “#” for groups, giving BarCamp—a technology unconference—as the example.

Twitter did not immediately adopt hashtags as an official feature. The convention spread organically, especially during the 2007 San Diego forest fires, when users added location-based tags to make updates easier to find. Twitter later built hashtag recognition and search into the platform.

A common mix-up is confusing the first hashtag, #barcamp, with #sandiegofire, which became one of the earliest widely used hashtags for breaking news. The term “hash tag” itself was popularized separately in a blog post by Stowe Boyd on August 26, 2007.