license, in public law, permission by legal authority to engage in certain acts and also the document showing such permission. Some licenses are required for the protection of the public; they assure professional competence (e.g., physicians) or moral fitness (e.g., tavern keepers). Others are designed primarily to raise revenue or to keep a registry (e.g., automobile licenses). It is a crime to engage in a licensed activity without having first procured a license. In property law, a license is a right that the owner grants some other party to make use of his land. Such licenses are revocable at will if they are not part of a contract. They are personal and hence may not be sold; they expire on the death of the grantee. A license to cross another's land is an easement in gross. In patent law, a license is a written authority granted by the owner of a patent to another person, empowering the latter to make or use the patented article for a limited period or in a limited territory.