The history of the # (hash) symbol

HashtagWhen Twitter was launched in 2006 it was very basic in comparison to what it is today. Its first users were asked to simply share updates with their friends and colleagues in response to a simple question: ‘What are you doing?’ (Burgess, 2015). The platform had no extended functionalities as we know them today and these were only developed over the years mostly via user-led innovations, and only later were integrated into the architecture of the system (Bruns and Burgess, 2015:16).

Examples of these user led innovations include @replies (see similarities with IRC chanops), used as cross-referencing functionality for addressing or mentioning other users ; the integration of multimedia uploads into the platform and lastly – hashtags (definitions) – a simple tool to organise content on Twitter.

The history of the # symbol

The pound sign (in American English) or hash symbol has a long history of usage in the Information Technology, most of the time as a tool to highlight a special meaning. One of # first uses was very technical and it took place in 1970 in the assembly language of the PDP-11 as #N to indicate immediate mode, where N could be ‘a number, user defined symbol or expression’ (Online: 2011).

Almost a decade later # was used again for special keywords in the C programming language (Kernighan and Ritchie: 1978: 86). Then finally in 1993 it reappeared on IRC as one of the four special characters: ‘&’, ‘#’, ‘+’ or ‘!’ known as IRC ‘channel prefixes’. These prefixes had to be followed by characters (letters or numbers) which as a result formed IRC channels, defined as ‘named groups of one or more clients which all receive messages addressed to that channel’ (Kalt 2000: Online).

The creation and administration of channels on IRC was very simple. A channel was created immediately when the first user joined it, and ceased to exist when the last user left it. During their existence any user (or client as they were called) was allowed to ‘reference the channel’ using the name of the channel. Interestingly, the user who created the channel automatically become channel operator (also known as a “chop” or “chanop”) and was considered to ‘own’ that channel. Chanops were also identified by the ‘@’ symbol next to their nickname whenever it is associated with a channel (Kalt, C. 2000: Online, Oikarinen and Reed 1993: Online).

The history of the # symbol on Twitter

On Twitter the # symbol was first used by San Francisco based Technologist Chris Messina (back then known on Twitter as @factoryjoe) on 23rd August 2007 in a short post which read: ‘how do you feel about using # (pound) for groups. As in #barcamp [msg]?’ (see Figure 1).

Figure 1: The historical first Tweet with a hashtag. Posted by Chris Messina on Twitter on 23 Aug 2007 [Last accessed on 28/08/2016] Available from: Twitter
Figure 1: The historical first Tweet with a hashtag. Posted by Chris Messina on Twitter on 23 Aug 2007 [Last accessed on 28/08/2016] Available from: Twitter
#barcamp – the first hashtag ever used

Two days later Messina commented on his blog (Messina 2007) that hashtags were a ‘rather messy proposal’ but also noticed that ‘ – there is certainly some merit to improving contextualization, content filtering and exploratory serendipity within Twitter. (by using them)’ In order to do this he suggested using ‘channel tags’ on Twitter in a way they were originally used on IRC – as tools allowing users to follow and contribute to conversations:

Every time someone uses a channel tag to mark a status, not only do we know something specific about that status, but others can eavesdrop on the context of it and then join in the channel and contribute as well. Rather than trying to ping-pong discussion between one or more individuals with daisy-chained @replies, using a simple #reply means that people not in the @reply queue will be able to follow along, as people do with Flickr or Delicious tags. Furthermore, topics that enter into existing channels will become visible to those who have previously joined in the discussion. And, perhaps best of all, anyone can choose to leave or remove topics that don’t interest them. (Messina 2007)

Messina’s above simple explanation of hashtags shows how skilfully he combined the special meaning of IRC channels and tagging techniques used on Flickr or Delicious in order to create one simple tool – a hashtag.

Useful links:

Cite this page:

Piatek, S. J. (2016) The history of the # (hash) symbol in S.J. Piatek Online [Online] Available at: [Accessed [enter date]]


Leave a Reply

Your email address will not be published. Required fields are marked *