Many people find they get a lot more from the Foundation Training workshop if they have already read the main text, "NonViolent Communication: A Language of Life" (SM) by Marshall Rosenberg (founder of Nonviolent Communication). For those that don't have the book, the following could provide a good grounding.
You can read Chapter 1 of Dr Rosenberg's book online.
There's a great summary of the book (more like a condensed version than a summary, actually!) at http://www.ayahuasca-wasi.com/english/articles/NVC.pdf
The Wikipedia entry is quite good: http://en.wikipedia.org/wiki/Nonviolent_Communication
Marshall Rosenberg on Nonviolent Communication (1 hour long)
There are also many, many NVC videos on YouTube - http://www.youtube.com/channel/HC1uDTDytAon4
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