The only time a law will not vary from state to state is if it is a federal law. There are certain bodies of common law (judge-made law) and certain uniform statutes that have been adopted in many or all states, but these laws still tend to have state-specific quirks that prevent them from being completely uniform across state lines.
Easement law is generally derived from common law. This means there are broad principles that are similar from state to state, but it is always a good idea to check with a local real estate professional (an attorney if you have a complex issue) to get the details of the laws that apply in your state. Having said, here are the general principles that should apply in all states.
An easement is a limited right to use another person’s land for a particular purpose. Easements can be appurtenant (run with the land) or they can be in gross (personal to a specific person). If an easement is personal to a specific landowner, then when that landowner sells the property, the easement terminates. If the easement runs with the land, when the owner of the land benefiting from the easement sells the land, ownership of the easement automatically transfers to the new owner.
Easements can be created in any of four ways. They can be created expressly wherein the owner of the land being used for the easement makes an express, written grant to another person. They can be created by reservation or exception wherein a landowner who is conveying his land reserves an easement to himself. Easements can be created by prescription, which is the rough equivalent to adverse possession, and easements can be created implication, which usually requires some sort of necessity.
The scope of an easement depends on the type. A grant of express easement or a reservation of an easement usually states the scope of the easement, though the use of the easement is allowed to change according to the times. The scope of an easement by prescription and the scope of an implied easement are both limited to the use being made of the easement.
An easement can be terminated if it expires; if its owner releases it; it its owner abandons it; or if the owner of the land served by the easement and the owner of the land over which the easement runs become the same person. This is called unity of title or extinguishment.
These are the general precepts of the law easement, and there are many more specific details that may vary from state to state. If you have a question about easement law, contact a real estate professional.