The Ordnung is a set of rules for Amish, Old Order Mennonite and Conservative Mennonite living. Ordnung (pronounced [ˈɔʁdnʊŋ] (listen)) is the German word for order, discipline, rule, arrangement, organization, or system. Because the Amish have no central church government, each assembly is autonomous and is its own governing authority. Thus, every local church maintains an individual set of rules, adhering to its own Ordnung, which may vary from district to district as each community administers its own guidelines. These rules are largely unwritten, yet they define the very essence of Amish identity. Conservative Mennonites refer to Ordnung by the English terms "discipline" or "standard" and are usually written.

The Amish blueprint for expected behavior, called the Ordnung, regulates private, public, and ceremonial life. Ordnung does not translate readily into English. Sometimes rendered as ordinance or discipline, the Ordnung is best thought of as an ordering of the whole way of life ... a code of conduct which the church maintains by tradition rather than by systematic or explicit rules. A member noted: The order is not written down. The people just know it, that's all. Rather than a packet of rules to memorize, the Ordnung is the understood behavior by which the Amish are expected to live. In the same way that the rules of grammar are learned by children, so the Ordnung, the grammar of order, is learned by Amish youth. The Ordnung evolved gradually over the decades as the church sought to strike a delicate balance between tradition and change. Specific details of the Ordnung vary across church districts and settlements.