Differential assessment programs for farmland started as an experiment in a few States in the late fifties, expanding to 48 States by 1979. The legislation was intended to provide tax relief to farmers and help preserve farmland by assessing farms at their agricultural value, rather than market value. As these laws became widespread, each State developed a slightly different set of provisions. It is, therefore, difficult to classify them in a few general categories. But, there are three broad types: preferential assessment, deferred tax, and restrictive agreement. Some States have more than one type.