Licensee estoppel
Licensee estoppel was a U.S. patent law doctrine, now overturned, that a licensee under a patent would not be permitted to challenge the validity of the patent. The Supreme Court, in Lear, Inc. v. Adkins (1969), held the doctrine inconsistent with a federal policy that the invalidity of specious patents should be unmasked in order to permit full and free competition in technology ideas that belong in the public domain.