The law of future interests is a legal device that has evolved to ensure that the holder of future interests can enjoy property rights at some future time or on the happening of some future event. Future interests permit ownership to be shared among generations, allowing for a flexible transfer of property rights that is not possible in countries rooted in Roman law tradition. However, the law of future interests reflected the old idea of ​​land law in medieval feudal society, and as a complex legal device, was subject to reform in modern American society through a simplification process. Today, it is rare to transfer a legal freehold estate in land other than fee simple. Accordingly, legal future interests in real property are uncommon, and the importance of future interests in this area has been diminishing. Future interests remain important as a means of enabling flexible estate planning. However, as the concept of existing land-oriented important assets expands to stocks, bonds, or other human property, future interests are becoming more widely utilized, primarily as a means of managing and disposing of personal property through trust. Although the law of future interests began with the formation of land tenure in the medieval feudal society, it is mostly used today for succession of family property through trust, which is one of the very important basic concepts of comparative legal research.