You can divide the environments we spend our time in into three catagories - where we work, where we live and where we socialise. It is usually in the latter environment that we find a sense of membership in a community, through interacting with friends. Years ago, places like local pubs, barber shops and cafes provided places where people could meet and socialise, but in today's modern world these places are becoming increasingly rare, and it is becoming harder and harder for people to find and participate in any such community.
So is it any suprise that so many people have turned to the internet to provide a sense of community, when the real world is becoming more and more ephemeral? It's far easier to find people with common interests online than it is in the real world, and even those with minority interests are likely to be able to find like-minded people spread across the globe.
In addition there is little risk of rejection online compared to in the real world - joining an online community is often relatively painless. When meeting people in real life it is the first fifteen seconds or so that count the most towards their opinion of you - online, the only information about yourself that is available is that which you choose to give out, leaving what you say as the only real means of judging you.
Early versions of online communities began to appear in the 70s and 80s. The first was the Community Memory project in Berkeley, founded in the early 70s. It relied on the use of coin-operated public terminals, and provided anonymous posting and the creation of forums to anybody who wanted to use the system. However this system wasn't connected to any outside networks, and as such served mainly as an extension to an already existing community.
In the 80s the idea of online communities grew, with places like The WELL and Cleveland Free-Net, but again in these cases, the core of the community was locally based. There are several other such local online communities around the world.
However it is really with the huge growth of people who have access to the internet over the last two decades or so that truly online communities have arisen. The first place this occured was on USENET, in which people could find a newsgroup for a vast array of subjects and engage in conversations with people across the world. Communities based on shared interests formed around particular newsgroups, and people would establish online identities and get to know the other people who participated. Despite the faceless nature of the net, bonds were formed as strong as those that can be found in the real world, with many people meeting in real life with people they had got to know online.
In more recent years new mediums have arisen on the internet, allowing new communities to form. The somewhat chaotic IRC network allows real-time chat between people online, making it closer to real life in some ways. The explosive growth of the web has given rise to the weblog, of which Slashdot is an early example, creating a community where users could discuss issues that interested them. Although somewhat fractured now, nobody can argue that Slashdot had a very well developed community of people with shared interests.
So as more and more people get online, the potential for more and more communities will develop. How do you see these communities developing? Will they become larger as more people discover them or do you think that in the longer-term the trend will be towards smaller, more focused communities? Will they remain as open as possible, or attempt to restrict their "membership" to a chosen demographic, much as Advogato does? And how much will this influence what goes on in the real world? Many people already feel more confortable in online communities than they do offline, and it's quite possible that this lure will grow stronger in coming years.