1. Invite-only. Any attendee can recommend a future attendee to be invited, so this is not about elitism rather that attendees add to to a two-way conversation, not simply sit and receive information.
2. Unconference format. On the first night everyone sits down to dinner, figures out the most important topics to discuss, and volunteers themselves to lead or join workshops on the topic. The conference schedule only comes into being on the first day.
3. Suburban location. The venues are invariably 40-60 minutes outside a major city, easy for international guests, yet harder for attendees to wander off into the city during the day (or even at night).
4. Free to attend. The events are sponsored by Google and The Knight Foundation who do a pretty good job of hanging back, being supportive and not imposing any agenda. Attendee costs are limited to travel and accommodation.
5. Weekend timing. Starting on a Friday ending on a Sunday ensures an informal approach and gets people out of their work and home comfort zones.
6. Werewolf. Daytime discussions invariably merge into dinner and then on to organised games of Werewolf to the late hours, hugely increasing camaraderie, intensity, socialization, truth-telling (eventually) and so on.