In classical economics economic rent is a residual value that remains after all costs of production (including a reasonable profit) have been covered.
Many economists, therefore, have been arguing that this residual value is the proper source of public revenue. Since it is not the result of the effort of worker, owner, or entrepreneur, it does not penalise and depress productive effort like conventional taxation.

Economic rent arises with all natural resources; not only land but anything under, on, and above land that exists in nature without the intervention of human ingenuity. Furthermore, technological advance reveals new natural resources which were not known, or were not worth exploiting, before. Airport landing slots, and the electromagnetic spectrum are the most obvious twentieth century example. Also, oil fields in many parts of the world were only a nuisance to farmers before the internal combustion engine technology created a quadrillion dollar demand for oil.