ResourceCentre > Glossary > Opt-out and Opt-in collective actions
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Opt-out collective action, once the class/group is certified, includes all those class members who have not opted out. See for instance the U.S. Class action model.
Opt-in collective action requires an act of opting in for a potential class/group member to become formally a class/group member. Most European collective litigation models (see link to our national collective litigation models section) are opt-in procedures.