Evergreen is an English language term for a tree or plant that does not shed its leaves in autumn. Evergreening of a patent refers to tactics used by patent holders, particularly in the pharmaceutical industry designed to extend the period of patent protection for a product beyond the 20 years from the application date generally guaranteed in law.
Various tactics are used to evergreen, such as Orphan Drug Rights, patents on delivery methods, patents on formulations developed during the initial patent term, patent term extensions. Evergreening of patents is becoming increasingly controversial.