The Donner Party (sometimes called the Donner–Reed Party) was a group of American pioneers who migrated to California in a wagon train from the Midwest. Delayed by a multitude of mishaps, they spent the winter of 1846–1847 snowbound in the Sierra Nevada mountain range. Some of the migrants resorted to cannibalism to survive, eating the bodies of those who had succumbed to starvation, sickness, and extreme cold.

The Donner Party departed Missouri on the Oregon Trail in the spring of 1846, behind many other pioneer families who were attempting to make the same overland trip. The journey west usually took between four and six months, but the Donner Party was slowed after electing to follow a new route called the Hastings Cutoff, which bypassed established trails and instead crossed the Rocky Mountains' Wasatch Range and the Great Salt Lake Desert in present-day Utah. The desolate and rugged terrain, and the difficulties they later encountered while traveling along the Humboldt River in present-day Nevada, resulted in the loss of many cattle and wagons, and divisions soon formed within the group.

By early November, the migrants had reached the Sierra Nevada but became trapped by an early, heavy snowfall near Truckee Lake (now Donner Lake) high in the mountains. Their food supplies ran dangerously low, and in mid-December some of the group set out on foot to obtain help. Rescuers from California attempted to reach the migrants, but the first relief party did not arrive until the middle of February 1847, almost four months after the wagon train became trapped. Of the 87 members of the party, 48 survived the ordeal. Historians have described the episode as one of the most fascinating tragedies in California history and in the entire record of American westward migration.