The concept of natural resource rents is much used in the natural resource economics literature. It is therefore somewhat surprising that in this same literature it is difficult to find a clear definition of the concept. Possibly as a result, the concept is often loosely employed and in some texts it appears to be taken to be virtually synonymous with profits. The paper provides a definition of the concept of natural resource rents that is both unambiguous and in conformance with the more traditional concept of economic. A general expression for natural resource rents is derived as a function of the resource stock level, the rate of resource use and, its properties explored.