IRC Section 2037 requires inclusion in the gross estate of any interest in property transferred by the decedent if both of the following conditions are met:
(1) Possession or enjoyment of the property can, through ownership of the transferred interest, be obtained only by surviving the decedent; and
(2) The decedent has retained a reversionary interest in the property which, immediately before his death, exceeded 5 percent of the value of the property.
A simple example would be a transfer to an irrevocable living trust under the following terms: income to grantor’s wife for her life; property to revert to grantor if living at wife’s death and if not, property to their daughter.