Under the exhaustion doctrine (also called the first sale doctrine and patent exhaustion), the first unrestricted sale of a patented item exhausts the patentee's control over that particular item. It generally is asserted as an affirmative defense to charges of patent infringement, but less commonly is asserted affirmatively in a declaratory judgment action. It is closely related to (and sometimes conflated with) the doctrine of implied license, and is often asserted in conjunction with claims of equitable estoppel or legal estoppel.