I do a lot before an event. Infact it is the most critical work I do. I work with the host executive or manager about the theme for sure, but also about the extent of openness that they want. I ask them to clarify the parameters within which people are free to self-organize and act. If it is a large event, I have meet with a whole senior team for a day to explore these issues or to hold an "small space" event about a key issue so that they know what they are getting into. If they want to control the discussion, I propose other meeting approaches.
Larry
