Old Faithful is the world's most famous geyser and Yellowstone's icon. It erupts every 60-110 minutes with remarkable regularity for over 100 years. Boiling water reaches 100-180 feet high and eruptions last 1.5-5 minutes. Rangers predict the next eruption with 90% accuracy within a 10-minute window. The new Visitor Education Center features exhibits on hydrothermal phenomena. About 20 eruptions occur daily, making it easy to witness this natural wonder.