Implied license

An implied license is an unwritten license which permits a party (the licensee) to do something that would normally require the express permission of another party (the licensor). Implied licenses may arise by operation of law from actions by the licensor which lead the licensee to believe that it has the necessary permission.
Implied licenses often arise where the licensee has purchased a physical embodiment of some intellectual property belonging to the licensor, or has paid for its creation, but has not obtained permission to use the intellectual property.
Implication: from surrounding circumstances or by operation of law?
In the United States, implied licenses are usually considered to be of two kinds: either they reflect the intention of the parties, which is inferred from a fact-specific inquiry into the surrounding circumstances, or else they are constructive agreements, in which case the intention of the parties is likely to be immaterial. In reality, there is a continuum between these kinds of implied license and it may be difficult to determine whether the license or contract in question is one which the law implies, irrespective of any protests by the unwilling licensor, or instead one inferred from the whole pattern of factual circumstances including the evidence of intent.
In England, there is more of a tendency to regard all implied licenses as matters of fact and intent, while what would be a license implied by law in the US is treated under some other branch of substantive law such as the doctrine of non-derogation from grants.
In both countries, the exhaustion doctrine has the effect of creating an implied license to use a product sold under the "authority" of the patentee. It is controversial whether and to what extent contractual expedients can successfully limit the scope of such implied licenses.
Express license.
The opposite of an implied license is an "express license", which, for some forms of intellectual property, must be in writing. Oral exclusive licenses were permitted, however, under US copyright law before 1978. Oral nonexclusive copyright licenses remain valid under US law. Patent licenses may be oral. Licenses under the Semiconductor Chip Protection Act must be in writing.