Just compensation

Just compensation is required to be paid by the Fifth Amendment to the U.S. Constitution (and counterpart state constitutions) when private property is taken (or in some states, damaged then Inverse Condemnation is the relevant description of eminent domain) for public use. For reasons of expedience, courts have been generally using fair market value as the measure of just compensation, reasoning that this is the amount that a willing seller would accept in a voluntary sales transaction and therefore it should also be payable in an involuntary one. However, the U.S. Supreme Court has repeatedly acknowledged that "fair market value" as defined by it falls short of what sellers would demand and receive in voluntary transactions.