Kim Sbarcea has pointed to some very useful introductory resources on communities of practice. To quote:
Once again, I find myself in need of explaining CoPs (communities of practice) to people I’m working with. I’ve been working with CoPs since 2002 in the same organisation. There’s been the usual ups and downs – a couple of CoPs bit the dust (really because they’d reached the limits of their purpose); senior management have tried to get their claws into the CoPs or grilled me over ROI on the CoPs; and the CoPs have survived a recent restructure.