Unjust enrichment

The retention of a benefit conferred by another, that is not intended as a gift and is not legally justifiable, without offering compensation, in circumstances where compensation is reasonably expected. 

The elements of a cause of action for unjust enrichment are:  the enrichment of the party accused of unjust enrichment; that such enrichment was at the expense of the party seeking [wex:restitution]; and the circumstances were such that in [wex:equity] and good conscience restitution should be made.  An additional requirement is that the party accused of unjust enrichment must know of the benefit conferred; to ensure that the benefit was not foisted on the recipient and is something for which compensation is reasonably expected.

Recovery on a theory of unjust enrichment typically occurs where there was no contract between the parties, or a contract turns out to be invalid.  See [wex:quasi-contract].