An oral law is a code of conduct in use in a given culture, religion or community application, by which a body of rules of human behaviour is transmitted by oral tradition and effectively respected, or the single rule that is orally transmitted.

Many cultures have an oral law, while most contemporary legal systems have a formal written organisation. The oral tradition (from the Latin tradere = to transmit) is the typical instrument of transmission of the oral codes or, in a more general sense, is the complex of what a culture transmits of itself among the generations, "from father to son". This kind of transmission can be due to lack of other means, such as in illiterate or criminal societies, or can be expressly required by the same law.

There has been a continuous debate over oral versus written transmission, with the focus on the perceived higher reliability of written evidence, primarily based on the "linear world of academia" where only written down records are accepted. However, "standard" theories of orality and literacy have been proposed.