Well, I've never been involved in one, but from what I have gathered from reading the blogs of others who have taken part, a small group of quilters agree on some basics and then it starts with a center block. Each quilter makes a center block. Then the block is passed to the next person for a border of sorts, and so on, until it has gone to each quilter, and then it goes back to the original quilter. I'll see if I can get more info sometime.