Legal Definitions - mutuality of parties

Definition: The mutuality of parties refers to the requirement that both parties must have been in privity with one another in an earlier proceeding to bar a party from relitigating an issue determined against that party in an earlier action. This is also known as the mutuality doctrine.

Example: If a person sues a company and loses, they cannot sue the same company again for the same issue if the company was also a party in the first lawsuit. This is because both parties were in privity with each other in the first lawsuit, and the mutuality of parties doctrine prevents the person from relitigating the same issue.

This doctrine ensures that both parties have an equal opportunity to present their case and that the outcome of the first lawsuit is final and binding for both parties.