Feudal land tenure in England

Under the English feudal system several different forms of land tenure existed, each effectively a contract with differing rights and duties attached thereto. Such tenures could be either free-hold, signifying that they were hereditable or perpetual, or non-free where the tenancy terminated on the tenant's death or at an earlier specified period.
High medieval period.
In England's ancient past large parts of the realm were unoccupied and owned as allodial titles, the land owners simply cooperated with the king out of a mutual interest instead of legal obligation. It wasn't until the Norman conquest when William the Conqueror declared himself to be the sole allodial owner of all of the realm that land tenures changed drastically. In William's kingdom the common exchange and sale of land became restricted and all landholders were made to provide a service to their lord ("no land without a lord").
Norman reforms.
William stripped the land from those who opposed him and redistributed it between his followers. He introduced a new type of feudalism in which obligation continued to all the way down the hierarchy which was inspired by the military system.
Barony and knight-service.
The tenant-in-chiefs held their land by the tenure of barony which required the tenant to provide a number of knights for their liege for 40 days per annum, after the served days the liege was either forced to begin paying the knights or dismiss them. However, tenants who held their land the tenure of knight-service were not to pass their lands to the heir automatically but required the lord's approval.
The system however proved difficult to sustain as the assessment of knight's fees became impossible to maintain for few properties retained the same wealth and population as they did when they were first enfeoffed leading to a situation where the lord only had provided a marginal number of knights of what he actually could muster. Another issue was the practice of subinfeudation in which the subtenants would alienate the land to tenants of their own, it became unpopular amongst the superior lords and was banned by Edward I in Quia Emptores, as a compensation sale of properties was made legal.
Late medieval period.
Over the course of the late medieval period knight-service came to be replaced by the tenure of scutage in which tenants paid tax according to their knight's fee instead of providing knights. Before the mid-13th century the fiefs hadn't been inheritable due to fear that the heir of the tenant couldn't provide the knight-service, however, due to scutage replacing knight-service, that fear no longer existed; the heirs were allowed to succeeded fiefs in exchange of paying a type of inheritance tax.
Tenures Abolition Act 1660 declared that all land was to be held by socage tenure, ending the feudal tenure.