The Doctrine of Exchange is a central tenet of Scientology, which dictates that for spiritual well-being, "anytime a person receives something, he must pay something back" and balance "inflow" with "outflow". The Church of Scientology has presented this as the reason why some of its services, such as auditing (a central practice, and sometimes described as the central practice of Scientology), must never be given away, to members who are at the church, but must be paid for. This is frequently used by the Church as an explanation for the fixed pricing of its many fees.
The Church of Scientology has argued in its requests for tax exemption that Scientology courses must have fixed fees - a practice that otherwise goes against the prohibition of quid pro quo transactions in tax-exempt organizations - because of this religious doctrine.
Not all services fall under the Doctrine. The Church has identified some services as examples of services where "no donation is expected from members": 
- Listening to lectures, whether from fellow parishioners or playings of L. Ron Hubbard’s lectures on tape
- Reading Scientology scripture in the Church library
- Meeting with fellow parishioners
- Receiving counseling (but not auditing) from a Scientology chaplain
- Attending Sunday services, sermons, weddings, christenings or funerals
- ↑ 1.0 1.1 Hernandez v. Commissioner, U.S. Supreme Court
- ↑ http://www.usdoj.gov/osg/briefs/1988/sg880419.txt
- ↑ Scientology Counselling - The Practice of Scientology
- ↑ "Scientology Today : How are Churches of Scientology supported financially?". Church of Scientology. http://www.scientologytoday.org/Common/question/pg35.htm. Retrieved 2006-09-22.