Plan far ahead. Although the inn is huge, it is also extremely popular. If you want to get a good (newer) room, you will need to reserve a year in advance, especially if you are traveling during the summer months.
Adjust your preferences. Some of the older rooms do not have private baths, but they might be all that is available if you reserve "late" (less than three months before your trip).
Be flexible. You are more likely to get a good room if you are willing to travel and stay during the off-season and during weekdays.
Call the Inn directly. Dial (866) GEYSERLAND or (866) 439-7375 to request a reservation.
Check online. Visit the Old Faithful Inn's website to check availability and to register (see Resources). On the left side of the site, there is a drop-down menu where you can select the dates and type of room you wish to reserve.
Call the Yellowstone National Park lodging line. Dial (307) 344-7901 to request a reservation. Be sure to clarify that you are asking for rooms at the Old Faithful Inn, as this number accepts reservations for all park lodging.