Farming is a technique of financial management, namely the process of commuting (changing), by its assignment by legal contract to a third party, a future uncertain revenue stream into fixed and certain periodic rents, in consideration for which commutation a discount in value received is suffered. It is most commonly used in the field of public finance where the state wishes to gain some certainty about its future taxation revenue for the purposes of medium-term budgetting of expenditure. The tax collection process requires considerable expenditure on administration and the yield is uncertain both as to amount and timing, as taxpayers delay or default on their assessed obligations, often the result of unforeseen external forces such as bad weather affecting harvests. Governments (the lessors) have thus frequently over history resorted to the services of an entrepreneurial financier (the tenant) to whom they lease or assign the right to collect and retain the whole of the tax revenue due to the state in return for his payment into the treasury of fixed sums (rent) in exchange.