The original idea was that if a public entity, such as a local city government, needed a piece of land, and the owner absolutely refused to sell, they could be forced to give it up at fair market value "for the common good."  Today, it is being most horribly abused, to condemn people's land so it can be used for commercial enterprises like shopping centers.  The Institute for Justice, which I think is www.ij.org, is on it.  This (and other Libertarian fights against injustice) matters so much to me that I've named the Institute for Justice as the contingent beneficiary in my will.  The fact that my estate is tiny is not the point; it's the thought that counts.  Besides, a hundred tiny estates could add up to a pretty fair chunk of money.