Before the development of written language in a given society, oral history has been the primary means of conveying information from one generation to the next. The most common form of this transmission is through storytelling and the recitation of epic poetry, with the stories and poems collectively known as the oral tradition of a people. The combination of this oral tradition with morals and rituals passed down by word of mouth is known as the folklore of a society. Although not as prevalent now as in the past, oral history is still very much alive among many North American native groups.
Because variations tend to be introduced into a tale with each repetition, the reliability of oral history is often called into doubt. However, the information passed on has occasionally shown a surprising accuracy over long periods of time. For example, the Iliad, an epic poem of Homer describing the conquest of Troy, was passed down as oral history from perhaps the eighth century BCE, until being recorded in writing by Pisistratos. Nonetheless, factual elements of the Iliad were at least partially validated by the discovery of ruins discovered by Heinrich Schliemann in 1870, thought to be those of the city described in the poem.
The most popular examples of oral history are the works of several authors that have, over the span of many hundred years BCE, collected folklore which ultimately resulted in these works being included in a collective book known as the Old Testament. The New Testament was created by four different original authors whose slightly differing versions of many biblical events were combined. The Bible was therefore 'nearly' entirely created using oral history.
Oral history is also used to refer to recording eyewitness accounts of historical events. Some anthropologists started collecting recordings (at first especially of American Indian folklore) on phonograph cylinders in the late 19th century. In the 1930s the United States Library of Congress started an oral history program to record traditional folk music, and accounts by surviving witnesses of the American Civil War, Slavery, and other major historical events, onto acetate discs. With the development of audio tape recordings the task of oral historians became easier.
One of the most important rules for those collecting oral history is to avoid asking leading questions, for many people will tend to say what they think the historian wants them to say.
Oral historians attempt to record the memories of many different people when researching a given event. Since any given individual may misremember events or distort their account for personal reasons, the historical documentation is considered to reside in the points of agreement of many different sources, rather than the account of any one person.
Oral history is now often used when historians investigate History from below.