Whom to invite: Everyone, ideally. After all, sometimes it’s the random second cousin you never thought would show up who ends up being the life of the party. If you can’t include every branch of the family tree, “the general rule of thumb is that you should decide the parameters first―whether you’ll invite first cousins, second cousins, or beyond―then include everyone that falls under that umbrella,” says Haltzman.
When to start planning: Set a date as early as possible, preferably a year in advance. Families with school-age children generally need to plan around the school schedule.
How long it should last: For an annual reunion, a weekend will suffice. If reunions don’t occur as regularly, plan a few extra days for those who can stay longer. But remember: “The longer a reunion lasts, the more space you should have to spread out,” says Scott Haltzman, a psychiatrist and the author of The Secrets of Happy Families ($25, amazon.com). “I don’t recommend sharing a small cabin if it’s a weeklong event.”
How to organize it: Pick a point person from each nuclear family so that wires don’t get crossed, and take an informal survey of what people are willing to spend and when they would like to go. For help in organizing your party—down to finding vendors and designing special T-shirts—try Punchbowl.com.