How long should a community of practice be expected to last?

There really is no set length of time that a community should last. In most cases, a community of practice starts without a clear sense of how long it will exist. It will last as long as members find value in their learning together. The intensity and relevance of this value are more important than the duration of the group. Some communities exist for a very short time and some last for years. Of course just one encounter will not make for a community: some level of sustained interaction is required over time. But a community should be allowed to disperse as soon as it has lived its usefulness.