To clarify the federal government's definitions of a churches and other religious institution, the Internal Revenue Service uses clearly-defined guidelines. Over the years, the IRS has revised this list in response to various court decisions. To define churches and other religious entities, some of the IRS guidelines consider whether or not an institution has:

• A distinct legal existence and religious history,
• A recognized creed and form of worship,
• Established places of worship
• A regular congregation and regular religious services, and
• an organization of ordained ministers

Most mainstream religions such as Catholicism, Judaism, and common Protestant sects fit easily within the IRS guidelines. However, churches that are less traditional sometimes face difficulty in meeting the federal government's definition.