Originally Posted by faithng
You've got to make reservations at least a year in advance. We were there in June of last year and I think we tried almost everything in the park in Dec/Jan and most everything was booked. Old Faithful Inn was definitely booked. We ended up staying outside the park in Montana.
I definitely made my reservations less than 12 months in advance (but greater than six!). If it's full, keep trying, people cancel all the time!