Bias in sources happens when information shows a one-sided or unfair view. It can appear in writing, images, or spoken accounts. Bias often comes from the beliefs or experiences of the person creating the source.

A writer may describe an event in a way that supports their own group or ideas. Some historical records leave out certain people or details. News reports, diaries, and official documents can all contain bias.

Historians study bias to better understand sources. Comparing different sources can help show a fuller picture of past events.