In the common law of real property, any type of right to control or possess real property is called an estate. There are many types of estates, each of which gives a different sort of interest in the land. If that land interest begins in the future at the occurrence of an event that is not certain to occur, it is called a contingent estate. This sort of land interest is called a contingent estate because it comes into being only if some condition that is possible but not certain to happen occurs. The estate is therefore contingent on that future event taking place.
A contingent estate is a type of future interest in land. Future interests are those in which the right to possess or control the real property is not in effect yet but will arise in the future. If and when the particular condition takes place, that contingent estate will then come into effect. It is always possible, however, that this condition will not occur and that the contingent estate will never take effect.
Absolute legal possession and ownership of real property is called a fee interest in that property. The contingent estate generally grants a conditional fee interest in the land in question. It is conditional in the sense that when a certain condition takes place, the fee interest in the land is transferred to the contingent estate holder. The person who held the fee interest before that condition holds a determinable fee, also known as a fee simple determinable. That is a fee interest that can terminate when the relevant condition occurs.
One sort of contingent estate that once was fairly common was a grant of property "to A for life and then to the heirs of B." The heirs of person B in that case had a contingent estate called a contingent remainder. If person A died, the heirs of person B would take the fee interest in the land. That interest was contingent, however, on there being heirs of person B who were living at the time person A died. If person B had no heirs mother A died, the fee interest would transfer back to the original grantor or the grantor's heirs.
Originally, contingent estates were not alienable. In other words, they could not be sold or transferred. In the early 21st century, however, contingent estates are freely alienable in the United Kingdom and in most jurisdictions in the United States. A person is free to sell his or her possible future right to possess and control the property in question.